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#include <bits/stdc++.h>
using namespace std;

namespace std {

template<class Fun>
class y_combinator_result {
	Fun fun_;
public:
	template<class T>
	explicit y_combinator_result(T &&fun): fun_(std::forward<T>(fun)) {}

	template<class ...Args>
	decltype(auto) operator()(Args &&...args) {
		return fun_(std::ref(*this), std::forward<Args>(args)...);
	}
};

template<class Fun>
decltype(auto) y_combinator(Fun &&fun) {
	return y_combinator_result<std::decay_t<Fun>>(std::forward<Fun>(fun));
}

} // namespace std

namespace atcoder {

namespace internal {

// @param n `0 <= n`
// @return minimum non-negative `x` s.t. `n <= 2**x`
int ceil_pow2(int n) {
    int x = 0;
    while ((1U << x) < (unsigned int)(n)) x++;
    return x;
}

// @param n `1 <= n`
// @return minimum non-negative `x` s.t. `(n & (1 << x)) != 0`
constexpr int bsf_constexpr(unsigned int n) {
    int x = 0;
    while (!(n & (1 << x))) x++;
    return x;
}

// @param n `1 <= n`
// @return minimum non-negative `x` s.t. `(n & (1 << x)) != 0`
int bsf(unsigned int n) {
#ifdef _MSC_VER
    unsigned long index;
    _BitScanForward(&index, n);
    return index;
#else
    return __builtin_ctz(n);
#endif
}

}  // namespace internal

}  // namespace atcoder

namespace atcoder {

template <class S,
          S (*op)(S, S),
          S (*e)(),
          class F,
          S (*mapping)(F, S),
          F (*composition)(F, F),
          F (*id)()>
struct lazy_segtree {
  public:
    lazy_segtree() : lazy_segtree(0) {}
    explicit lazy_segtree(int n) : lazy_segtree(std::vector<S>(n, e())) {}
    explicit lazy_segtree(const std::vector<S>& v) : _n(int(v.size())) {
        log = internal::ceil_pow2(_n);
        size = 1 << log;
        d = std::vector<S>(2 * size, e());
        lz = std::vector<F>(size, id());
        for (int i = 0; i < _n; i++) d[size + i] = v[i];
        for (int i = size - 1; i >= 1; i--) {
            update(i);
        }
    }

    void set(int p, S x) {
        assert(0 <= p && p < _n);
        p += size;
        for (int i = log; i >= 1; i--) push(p >> i);
        d[p] = x;
        for (int i = 1; i <= log; i++) update(p >> i);
    }

    S get(int p) {
        assert(0 <= p && p < _n);
        p += size;
        for (int i = log; i >= 1; i--) push(p >> i);
        return d[p];
    }

    S prod(int l, int r) {
        assert(0 <= l && l <= r && r <= _n);
        if (l == r) return e();

        l += size;
        r += size;

        for (int i = log; i >= 1; i--) {
            if (((l >> i) << i) != l) push(l >> i);
            if (((r >> i) << i) != r) push((r - 1) >> i);
        }

        S sml = e(), smr = e();
        while (l < r) {
            if (l & 1) sml = op(sml, d[l++]);
            if (r & 1) smr = op(d[--r], smr);
            l >>= 1;
            r >>= 1;
        }

        return op(sml, smr);
    }

    S all_prod() { return d[1]; }

    void apply(int p, F f) {
        assert(0 <= p && p < _n);
        p += size;
        for (int i = log; i >= 1; i--) push(p >> i);
        d[p] = mapping(f, d[p]);
        for (int i = 1; i <= log; i++) update(p >> i);
    }
    void apply(int l, int r, F f) {
        assert(0 <= l && l <= r && r <= _n);
        if (l == r) return;

        l += size;
        r += size;

        for (int i = log; i >= 1; i--) {
            if (((l >> i) << i) != l) push(l >> i);
            if (((r >> i) << i) != r) push((r - 1) >> i);
        }

        {
            int l2 = l, r2 = r;
            while (l < r) {
                if (l & 1) all_apply(l++, f);
                if (r & 1) all_apply(--r, f);
                l >>= 1;
                r >>= 1;
            }
            l = l2;
            r = r2;
        }

        for (int i = 1; i <= log; i++) {
            if (((l >> i) << i) != l) update(l >> i);
            if (((r >> i) << i) != r) update((r - 1) >> i);
        }
    }

    template <bool (*g)(S)> int max_right(int l) {
        return max_right(l, [](S x) { return g(x); });
    }
    template <class G> int max_right(int l, G g) {
        assert(0 <= l && l <= _n);
        assert(g(e()));
        if (l == _n) return _n;
        l += size;
        for (int i = log; i >= 1; i--) push(l >> i);
        S sm = e();
        do {
            while (l % 2 == 0) l >>= 1;
            if (!g(op(sm, d[l]))) {
                while (l < size) {
                    push(l);
                    l = (2 * l);
                    if (g(op(sm, d[l]))) {
                        sm = op(sm, d[l]);
                        l++;
                    }
                }
                return l - size;
            }
            sm = op(sm, d[l]);
            l++;
        } while ((l & -l) != l);
        return _n;
    }

    template <bool (*g)(S)> int min_left(int r) {
        return min_left(r, [](S x) { return g(x); });
    }
    template <class G> int min_left(int r, G g) {
        assert(0 <= r && r <= _n);
        assert(g(e()));
        if (r == 0) return 0;
        r += size;
        for (int i = log; i >= 1; i--) push((r - 1) >> i);
        S sm = e();
        do {
            r--;
            while (r > 1 && (r % 2)) r >>= 1;
            if (!g(op(d[r], sm))) {
                while (r < size) {
                    push(r);
                    r = (2 * r + 1);
                    if (g(op(d[r], sm))) {
                        sm = op(d[r], sm);
                        r--;
                    }
                }
                return r + 1 - size;
            }
            sm = op(d[r], sm);
        } while ((r & -r) != r);
        return 0;
    }

  private:
    int _n, size, log;
    std::vector<S> d;
    std::vector<F> lz;

    void update(int k) { d[k] = op(d[2 * k], d[2 * k + 1]); }
    void all_apply(int k, F f) {
        d[k] = mapping(f, d[k]);
        if (k < size) lz[k] = composition(f, lz[k]);
    }
    void push(int k) {
        all_apply(2 * k, lz[k]);
        all_apply(2 * k + 1, lz[k]);
        lz[k] = id();
    }
};

}  // namespace atcoder

struct Frac { int p, q; };

template<class F>
Frac fracBS(F f, int N) {
	bool dir = 1, A = 1, B = 1;
	Frac lo{0, 1}, hi{1, 1}; // Set hi to 1/0 to search (0, N]
	if (f(lo)) return lo;
	assert(f(hi));
	while (A || B) {
		int adv = 0, step = 1; // move hi if dir, else lo
		for (int si = 0; step; (step *= 2) >>= si) {
			adv += step;
			Frac mid{lo.p * adv + hi.p, lo.q * adv + hi.q};
			if (abs(mid.p) > N || mid.q > N || dir == !f(mid)) {
				adv -= step; si = 2;
			}
		}
		hi.p += lo.p * adv;
		hi.q += lo.q * adv;
		dir = !dir;
		swap(lo, hi);
		A = B; B = !!adv;
	}
	return dir ? hi : lo;
}

using S = int;
using F = int;

S op(S x, S y) { return min(x, y); }
S e(){ return 10000; }
S mapping(F f, S x) { return f + x; }
F composition(F f, F g) { return f + g; }
F id() { return 0; }

int TESTS;
int CUR_TEST = 0;
void solve(){
	CUR_TEST++;
	int N;
	cin >> N;
	if(cin.peek() == '\n'){
		TESTS = N;
		cin >> N;
	}
	int L;
	cin >> L;
	vector<vector<int> > free(N, vector<int>(L));
	for(int i = 0; i < N; i++){
		for(int j = 0; j < L; j++){
			char c;
			cin >> c;
			assert(c == '.' || c == 'X');
			free[i][j] = c == '.';
		}
	}
	// if(CUR_TEST != 0){
	// 	return;
	// }
	// cerr << N << ' ' << L << '\n';
	// for(int i = 0; i < N; i++){
	// 	for(int j = 0; j < L; j++){
	// 		cerr << "X."[free[i][j]];
	// 	}
	// 	cerr << '\n';
	// }
	bool nonzero = true;
	for(int j = 0; j < L; j++){
		int nempty = 0;
		for(int i = 0; i < N; i++){
			if(free[i][j]) nempty++;
		}
		if(nempty == 0){
			nonzero = false;
		}
	}

    map<pair<int,int>, bool> memo;
	auto check = [&](int numerator, int denominator) -> bool {
        if(memo.count({numerator, denominator})) return memo[{numerator, denominator}];
		// cerr << "? " << numerator << "/" << denominator << '\n';
		int X = L * denominator;
		vector<vector<int> > A_psums(N, vector<int>(X+1));
		for(int i = 0; i < N; i++){
			for(int j = 0; j < X; j++){
				A_psums[i][j+1] = A_psums[i][j] + free[i][j / denominator];
			}
		}
		vector<int> cnt_vector(X);
		vector<int> has1_psum(X+1);
		for(int j = 0; j < X; j++){
			int cnt = 0;
			for(int i = 0; i < N; i++){
				cnt += free[i][j / denominator];
			}
			cnt_vector[j] = cnt;
			has1_psum[j+1] = has1_psum[j] + int(cnt <= 1);
		}
		int T = numerator;
		vector<vector<int> > next_allowed(N, vector<int>(X+1, X));
		for(int i = 0; i < N; i++){
			for(int j = X-1; j >= 0; j--){
				next_allowed[i][j] = next_allowed[i][j+1];
				if(j + T <= X && A_psums[i][j+T] - A_psums[i][j] == T && has1_psum[j+T] - has1_psum[j] == 0){
					next_allowed[i][j] = j;
				}
			}
		}
		atcoder::lazy_segtree<S, op, e, F, mapping, composition, id> seg(cnt_vector);
		vector<int> done(N, 0);
		int cur_time = 0;
		bool works = false;
		y_combinator([&](auto self, int k) -> void {
            if(works) return;
			if(k == N){
				works = true;
				return;
			}
			int m1 = -1, m2 = -1;
			for(int i = 0; i < N; i++){
				if(done[i] || next_allowed[i][cur_time] >= X) continue;
				if(m2 == -1 || next_allowed[i][cur_time] < next_allowed[m2][cur_time]) m2 = i;
				if(m1 == -1 || next_allowed[m2][cur_time] < next_allowed[m1][cur_time]) swap(m1, m2);
			}
            if(m2 != -1 && next_allowed[m2][cur_time] >= next_allowed[m1][cur_time] + T){
                m2 = -1;
            }
			for(int a : {m1, m2}){
				if(a == -1) continue;
                if(k+1 == N){
                    works = true;
                    continue;
                }
				int loc = next_allowed[a][cur_time];
				int prv_time = cur_time;
				// for(int i = 0; i < k; i++) cerr << ' ';
				// cerr << "try " << a << ' ' << loc << '\n';
				int new_bound = seg.min_left(loc + T, [&](int val){
					return val > 2;
				});
				new_bound = max(new_bound, loc);
                if(new_bound < X){
                    done[a] = 1;
                    cur_time = new_bound;
                    seg.apply(loc, loc + T, -1);
                    self(k+1);
                    seg.apply(loc, loc + T, 1);
                    cur_time = prv_time;
                    done[a] = 0;
                }
			}
		})(0);
        memo[{numerator, denominator}] = works;
		return works;
	};
	if(nonzero){
		int s = 0;
		int e = L+1;
		while(s + 1 < e){
			int mid = (s+e) / 2;
			bool works = check(mid, 1);
			(works ? s : e) = mid;
		}
        Frac bs_res = fracBS([&](Frac x){
            return check(x.q - x.p + x.q * s, x.q);
        }, N);
        pair<int,int> ans = {bs_res.q - bs_res.p + bs_res.q * s, bs_res.q};
		cout << ans.first << '/' << ans.second << '\n';
	} else {
		cout << -1 << '\n';
	}
}

int main(){
	ios_base::sync_with_stdio(false), cin.tie(nullptr);
	TESTS = 1;
	while(CUR_TEST < TESTS) solve();
}