// 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 = 100100;

int n, m, a[19][maxn], b[maxn], nxt[19][maxn], c[19][maxn], g[19][maxn];
pii fr[maxn << 5];
char s[19][maxn];

int p[19];
ll X, Y, f[19];

bool dfs(int d, int S) {
	if (d == n + 1) {
		return 1;
	}
	vector<int> cur;
	for (int i = 1; i <= n; ++i) {
		if (!(S & (1 << i))) {
			cur.pb(i);
		}
	}
	pii mn(1e18, 0), smn(1e18, 0);
	for (int i : cur) {
		ll t = f[d - 1];
		for (int j = 1; j <= d; ++j) {
			ll l = max(f[d - 1], j == 1 ? 0LL : f[j - 1] + X), r = (j < d ? f[j] + X : m * Y);
			if (l < r) {
				if (j == 1 && d - j + 2 == n + 1) {
					t = max(t, r);
					continue;
				}
				if (g[d - j + 2][l / Y + 1] >= (l + X + Y - 1) / Y - l / Y) {
					t = max(t, l);
				} else {
					t = max(t, min(r, (nxt[d - j + 2][l / Y + 2] - 1) * Y));
				}
			}
		}
		if (t % Y) {
			if (a[i][t / Y + 1] >= (t + X + Y - 1) / Y - t / Y) {
				pii x(t, i);
				if (x < mn) {
					smn = mn;
					mn = x;
				} else if (x < smn) {
					smn = x;
				}
				continue;
			} else {
				t += Y - t % Y;
			}
		}
		t = (c[i][t / Y + 1] - 1) * Y;
		if (t == m * Y) {
			return 0;
		}
		pii x(t, i);
		if (x < mn) {
			smn = mn;
			mn = x;
		} else if (x < smn) {
			smn = x;
		}
	}
	f[d] = mn.fst;
	p[d] = mn.scd;
	if (dfs(d + 1, S | (1 << mn.scd))) {
		return 1;
	}
	if (smn.scd) {
		f[d] = smn.fst;
		p[d] = smn.scd;
		if (dfs(d + 1, S | (1 << smn.scd))) {
			return 1;
		}
	}
	return 0;
}

inline bool check(ll x, ll y) {
	for (int i = 1; i <= n; ++i) {
		c[i][m + 1] = m + 1;
		for (int j = m; j; --j) {
			c[i][j] = (a[i][j] * y >= x ? j : c[i][j + 1]);
		}
	}
	for (int i = 1; i <= n; ++i) {
		nxt[i][m + 1] = m + 1;
		for (int j = m; j; --j) {
			g[i][j] = (b[j] >= i ? g[i][j + 1] + 1 : 0);
			nxt[i][j] = (g[i][j] * y >= x ? j : nxt[i][j + 1]);
		}
	}
	X = x;
	Y = y;
	f[0] = 0;
	return dfs(1, 0);
}

void solve() {
	scanf("%d%d", &n, &m);
	for (int i = 1; i <= n; ++i) {
		scanf("%s", s[i] + 1);
	}
	for (int i = 1; i <= m; ++i) {
		bool fl = 1;
		for (int j = 1; j <= n && fl; ++j) {
			fl &= (s[j][i] == 'X');
		}
		if (fl) {
			puts("-1");
			return;
		}
	}
	for (int i = 1; i <= n; ++i) {
		for (int j = m; j; --j) {
			a[i][j] = (s[i][j] == '.' ? a[i][j + 1] + 1 : 0);
			b[j] += (s[i][j] == '.');
		}
	}
	int tot = 0;
	for (int i = 1; i <= m; ++i) {
		for (int j = 1; j <= n; ++j) {
			if (__gcd(i, j) == 1) {
				fr[++tot] = mkp(i, j);
			}
		}
	}
	sort(fr + 1, fr + tot + 1, [&](const pii &a, const pii &b) {
		return a.fst * b.scd < b.fst * a.scd;
	});
	int l = 1, r = tot, ans = -1;
	while (l <= r) {
		int mid = (l + r) >> 1;
		if (check(fr[mid].fst, fr[mid].scd)) {
			ans = mid;
			l = mid + 1;
		} else {
			r = mid - 1;
		}
	}
	if (ans == -1) {
		puts("0/1");
		return;
	}
	printf("%lld/%lld\n", fr[ans].fst, fr[ans].scd);
}

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