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

#define rep(i, b, e) for(int i = (b); i <= (e); i++)
#define per(i, b, e) for(int i = (e); i >= (b); i--)
#define FOR(i, b, e) rep(i, b, (e) - 1)
#define SZ(x) int(x.size())
#define all(x) x.begin(), x.end()
#define pb push_back
#define mp make_pair
#define st first
#define nd second
using ll = long long;
using vi = vector<int>;
using pii = pair<int, int>;

auto &operator<<(auto &o, pair<auto, auto> p) {
    return o << "(" << p.st << ", " << p.nd << ")"; }
auto operator<<(auto &o, auto x)->decltype(end(x), o) {
    o << "{"; int i=0; for(auto e: x) o << ", " + 2*!i++ << e;
    return o << "}"; }
#ifdef LOCAL
#define deb(x...) cerr << "[" #x "]: ", [](auto...$) { \
    ((cerr << $ << "; "),...) << endl; }(x)
#else
#define deb(...)
#endif

#define LSB(x) ((x)&(-x))

vi dal, rem;
vector<pii> rangeW;
vector<vi> jestem;
int RR;

bool pick(int kt) {
    if(kt < 0) return 1;
    FOR(x, 0, RR) {
        bool good = 1;
        for(auto &id: jestem[kt]) {
            int satisfy = x <= rangeW[id].st || x >= rangeW[id].nd;
            if(dal[id] + satisfy == 0 && rem[id] == 1) {
                good = 0;
                break;
            }
        }
        if(!good) continue;
        for(auto &id: jestem[kt]) {
            dal[id] += x <= rangeW[id].st || x >= rangeW[id].nd;
            rem[id]--;
        }
        if(pick(kt - 1)) return 1;
        for(auto &id: jestem[kt]) {
            dal[id] -= x <= rangeW[id].st || x >= rangeW[id].nd;
            rem[id]++;
        }
    }
    return 0;
}

bool check(pii ulamek, vector<string> &s) {
    int n = SZ(s), L = SZ(s[0]);
    auto [d, scale] = ulamek;
    dal = rem = {};
    rangeW = {};
    jestem = vector<vi>(n);
    int full = (1 << n) - 1;
    auto dodajJestem = [](int mask) {
        for(int mk = mask; mk; mk ^= LSB(mk)) {
            jestem[__builtin_ctz(mk)].pb(SZ(dal));
        }
        dal.pb(0), rem.pb(__builtin_popcount(mask));
    };
    FOR(j, 0, L) {
        int kropki = 0;
        FOR(i, 0, n) if(s[i][j] == '.') kropki ^= 1 << i;
        FOR(k, 0, scale) {
            int me = j * scale + k;
            rangeW.pb({me - d, me + 1});
            dodajJestem(kropki);
            for(int mk = full ^ kropki; mk; mk ^= LSB(mk)) {
                rangeW.pb({me - d, me + 1});
                dodajJestem(LSB(mk));
            }
        }
    }
    RR = L * scale - d + 1;
    return pick(n - 1);
}

void solve() {
    int n, L;
    cin >> n >> L;
    vector<string> s(n);
    for(auto &x: s) cin >> x;
    FOR(j, 0, L) {
        bool good = 0;
        FOR(i, 0, n) good |= s[i][j] == '.';
        if(!good) {
            cout << "-1\n";
            return;
        }
    }
    vector<pii> ulamki;
    FOR(dol, 1, n + 1) FOR(gora, 0, L * dol + 1) {
        int a = gora, b = dol, g = gcd(gora, dol);
        ulamki.pb({a / g, b / g});
    }
    auto ulComp = [](const pii &a, const pii &b) {
        return a.st * b.nd < b.st * a.nd;
    };
    sort(all(ulamki), ulComp);
    ulamki.erase(unique(all(ulamki)), ulamki.end());
    int l = 0, r = SZ(ulamki);
    while(l + 1 < r) {
        int mid = (l + r) / 2;
        (check(ulamki[mid], s) ? l : r) = mid;
    }
    cout << ulamki[l].st << '/' << ulamki[l].nd << '\n';
}

int main() {
    cin.tie(0)->sync_with_stdio(0);
    int tt = 1;
    // cin >> tt;
    FOR(te, 0, tt) solve();
    return 0;
}