// Problem: P11921 [PA 2025] 看护 / Opieka
// Contest: Luogu
// URL: https://www.luogu.com.cn/problem/P11921
// Memory Limit: 1 MB
// Time Limit: 5000 ms
// 
// Powered by CP Editor (https://cpeditor.org)

#include <bits/stdc++.h>
#define pb emplace_back
#define fst first
#define scd second
#define mkp make_pair
#define mems(a, x) memset((a), (x), sizeof(a))

using namespace std;
typedef long long ll;
typedef double db;
typedef unsigned long long ull;
typedef long double ldb;
typedef pair<ll, ll> pii;

const int maxn = 1800100;

int n, m, f[(1 << 18) + 50];
char s[19][maxn], t[maxn];
int a[19][maxn], b[maxn];

inline bool check(int x) {
	mems(f, 0x3f);
	f[0] = 0;
	mems(b, 0);
	for (int i = 0; i < n; ++i) {
		for (int j = 1; j <= m; ++j) {
			a[i][j] = a[i][j - 1] + (s[i][j] == 'X');
			if (s[i][j] == '.') {
				++b[j];
			}
		}
	}
	for (int i = 1; i <= m; ++i) {
		b[i] = b[i - 1] + (b[i] <= 1);
	}
	for (int S = 0; S < (1 << n); ++S) {
		int v = f[S];
		if (v > m) {
			continue;
		}
		for (int i = 0; i < n; ++i) {
			if (S & (1 << i)) {
				continue;
			}
			for (int j = v; j + x <= m; ++j) {
				if (b[j + x] == b[j] && a[i][j + x] == a[i][j]) {
					f[S | (1 << i)] = min(f[S | (1 << i)], j + x);
					break;
				}
			}
		}
	}
	return f[(1 << n) - 1] <= m;
}

void solve() {
	scanf("%d%d", &n, &m);
	for (int i = 0; i < n; ++i) {
		scanf("%s", t + 1);
		int k = 0;
		for (int j = 1; j <= m; ++j) {
			for (int _ = 0; _ < n; ++_) {
				s[i][++k] = t[j];
			}
		}
	}
	m *= n;
	for (int i = 1; i <= m; ++i) {
		bool fl = 1;
		for (int j = 0; j < n && fl; ++j) {
			fl &= (s[j][i] == 'X');
		}
		if (fl) {
			puts("-1");
			return;
		}
	}
	int l = 1, r = m, ans = 0;
	while (l <= r) {
		int mid = (l + r) >> 1;
		if (check(mid)) {
			ans = mid;
			l = mid + 1;
		} else {
			r = mid - 1;
		}
	}
	int p = ans, q = n;
	int g = __gcd(p, q);
	p /= g;
	q /= g;
	printf("%d/%d\n", p, q);
}

int main() {
	int T = 1;
	// scanf("%d", &T);
	while (T--) {
		solve();
	}
	return 0;
}