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#include<bits/stdc++.h>
#define FOR(i,a,b) for(int i=a;i<b;++i)
#define FORD(i,a,b) for(int i=a;i>=b;--i)
#define PB push_back
#define EB emplace_back
#define FI first
#define SE second
#define umap unordered_map
#define uset unordered_set
#define vi vector<int>
#define vvi vector<vi>
#define vll vector<ll>
#define vvll vector<vll>
#define vpii vector<pii>
#define pii pair<ll, ll>
#define pll pair<ll, ll>
#define ALL(X) (X).begin(),(X).end()
#ifndef DEBUG
//#define endl (char)10
#endif
using namespace std;
using ll = long long;
using ld = long double;

template <class T>
ostream& operator<< (ostream& os, vector<T>& vec){
    for(auto& t : vec) os << t << " ";
    return os;
}
template<class T, class U>
ostream& operator<< (ostream& os, const pair<T, U>& p){
    os << p.FI << " " << p.SE;
    return os;
}
template<class T, class U>
istream& operator>> (istream& is, pair<T, U>& p){
    is >> p.FI >> p.SE;
    return is;
}
template <class T>
istream& operator>> (istream& is, vector<T>& vec){
    for(auto& p : vec) is >> p;
    return is;
}

/*

3 6
..X.XX
.X..X.
X..X..

*/

bool canrek(vector<string>& V, vi& wol, int r, int x, vi& pom, int idx) {
	if(idx == V.size()) return true;
	int m = V[0].size() * r;
	FOR(i,0,m-x+1) {
		bool ok = true;
		FOR(j,0,x) if (V[idx][(i + j) / r] == 'X' || wol[(i + j) / r] == pom[i + j] + 1) {
			i += j;
			ok = false;
			break;
		}
		if(!ok) continue;
		FOR(j,0,x) pom[i + j]++;
		if (canrek(V, wol, r, x, pom, idx + 1)) return true;
		FOR(j,0,x) pom[i + j]--;
	}
	return false;
}

bool can(vector<string>& V, vi& wol, int r, int x) {
	vi pom(V[0].size() * r, 0);
	return canrek(V, wol, r, x, pom, 0);
}

int solve(vector<string>& V, vi& wol, int r) {
	int b = 1, e = (V[0].size() * r / 2) + 2;
	while(b < e) {
		int x = (b + e) / 2;
		if(can(V, wol, r, x)) b = x + 1;
		else e = x;
	}
	return b - 1;
}

void st() {
	int n, m;
	cin >> n >> m;
	vector<string> V(n);
	cin >> V;
	vi wol(m, 0);
	FOR(i,0,m) {
		FOR(j,0,n) if (V[j][i] != 'X') wol[i]++;
		if(wol[i] == 0) {
			cout << -1 << endl;
			return;
		}
	}
	if(n == 1) {
		cout << "0/1" << endl;
		return;
	}
	int bl = 0, bm = 1;
	FOR(i,1+n/2,n+1){
		int c = solve(V, wol, i);
		if (c * bm > bl * i) {
			bl = c;
			bm = i;
		} 
	}
	int d = gcd(bl, bm);
	bl /= d;
	bm /= d;
	cout << bl << "/" << bm << endl;
}

int main () {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    int t = 1;
    //cin >> t;
    FOR(tid,0,t){
		//if(tid % 100000 == 0) cerr << tid << "/" << t << " = " << (double)(tid) / t * 100.0 << endl;
		st();
	}
}