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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

vector<string> przemnoz(vector<string>& os, int n, int l, int k) {
  vector<string> res(n);

  for (int i = 0; i < n; i++) {
    for (int j = 0; j < l; j++) {
      res[i] += string(k, os[i][j]);
    }
  }

  return res;
}

vector<string> os;
vector<int> ile;

bool mozna_wziac(int i, int idx, int l, int k) {
  if (idx + k > l) {
    return false;
  }
  for (int j = idx; j < idx + k; j++) {
    if (ile[j] <= 1) {
      return false;
    }
    if (os[i][j] == 'X') {
      return false;
    }
  }

  return true;
}

void wez(int idx, int k) {
  for (int j = idx; j < idx + k; j++) {
    ile[j]--;
  }
}
void oddaj(int idx, int k) {
  for (int j = idx; j < idx + k; j++) {
    ile[j]++;
  }
}

bool backtrack(int i, int n, int l, int k) {
  if (i == n) {
    return true;
  }

  for (int j = 0; j < l; j++) {
    if (mozna_wziac(i, j, l, k)) {
      wez(j, k);
      if (backtrack(i + 1, n, l, k)) {
        oddaj(j, k);
        deb(i, l, k, j);
        return true;
      }
      oddaj(j, k);
    }
  }

  return false;
}

int solve(int n, int l) {
  ile = vector<int>(l);
  for (int i = 0; i < l; i++) {
    for (int j = 0; j < n; j++) {
      ile[i] += (os[j][i] == '.');
    }
  }

  int lo = 0;
  int hi = l + 1;

  deb(n, l, os);
  // for (int i = 0; i < n; i++) {
  //   cerr << os[i] << "\n";
  // }

  while (lo < hi - 1) {
    int mid = (lo + hi) / 2;
    if (backtrack(0, n, l, mid)) {
      lo = mid;
    } else {
      hi = mid;
    }
  }

  return lo;
}

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie();

  int n, l;
  cin >> n >> l;

  vector<string> osoby(n);

  for (int i = 0; i < n; i++) {
    cin >> osoby[i];
  }

  for (int i = 0; i < l; i++) {
    int kto = -1;
    int il = 0;

    for (int j = 0; j < n; j++) {
      if (osoby[j][i] == '.') {
        kto = j;
        il++;
      }
    }

    if (il == 1) {
      osoby[kto][i] = 'X';
    }

    if (il == 0) {
      cout << -1 << "\n";
      return 0;
    }
  }

  int nom = 0;
  int den = 1;
  for (int i = 1; i <= n; i++) {
    os = przemnoz(osoby, n, l, i);
    int best = solve(n, l * i);

    // cout << i << ": " << best << "\n";

    if (best * den > nom * i) {
      nom = best;
      den = i;
    }
  }

  cout << nom << "/" << den << "\n";
}