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#ifndef LOCAL
#pragma GCC optimize("O3")
#endif
#include <bits/stdc++.h>
#define FOR(i,p,k) for(int i=(p);i<=(k);++i)
#define REP(i,n) FOR(i,0,(n)-1)
#define RFOR(i,p,n) for(int i=(p);i>=(n);--i)
#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()
#define ssize(x) int((x).size())
#define fi first
#define se second
#define V vector
#define pb push_back
#define eb emplace_back
#define C const
#define pn printf("\n")
using namespace std;
typedef long long ll;
typedef V<int> vi;
typedef V<ll> vll;
typedef const int ci;
typedef const ll cll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
void chmin(auto &a, auto b){a=min(a,b);}
void chmax(auto &a, auto b){a=max(a,b);}
ci inf = 2.1e9;
cll infll = 4.5e18;

int I(){
    int z;
    scanf("%d", &z);
    //cin >> z;
    return z;
}

void answer(){
    int n = I(), l = I();
    V wej(n, vi(l, 0));// jedynki to wolne
    REP(i, n){
        scanf("\n");
        REP(j, l){
            int c = getchar();
            wej[i][j] = c=='.';
        }
    }

    REP(i, l){
        int git = 0;
        REP(j, n) if(wej[j][i]) git = 1;
        if(!git){
            printf("-1\n");
            return;
        }
    }

    if(n == 1){
        printf("0/1\n");
        return;
    }

    if(n == 2){

    }

    auto xd = [&](V<vi> ciag, int k){
        int lmian = ssize(ciag[0]);
        vi dp(1<<lmian, 0);
        dp[0] = 1;
        for(vi vec : ciag){
            int maska_vec = 0;
            REP(i, lmian) maska_vec += vec[i]<<i;

            vi nowe(1<<lmian, 0);
            REP(i, lmian-k+1){
                int maska = maska_vec;
                int git = 1;
                REP(j, k){
                    if(!vec[i+j]){
                        git = 0;
                        break;
                    }
                    maska -= 1<<(i+j);
                }
                if(!git) continue;
                REP(stan, 1<<lmian) nowe[stan|maska] |= dp[stan];
            }
            swap(dp, nowe);
        }
        return dp.back();
    };

    auto rozstrzel = [&](int mian){
        int lmian = l*mian;
        V ciag(n, vi(lmian, 0));
        REP(i, n) REP(j, lmian) ciag[i][j] = wej[i][j/mian];
        return ciag;
    };
    /*
    if(!xd(rozstrzel(n), 1)){
        printf("0/1\n");
        return;
    }
    */

    pii wyn = {0, 1};
    pii nie_wyszlo = {l*(n+1)+1, n+1};
    FOR(mian, 1, n){
        int lmian = l*mian;
        auto ciag = rozstrzel(mian);

        int mam = 0;
        while((mam+1)*wyn.se <= wyn.fi*mian) ++mam;
        int wiecej = mam+1;
        if(!xd(ciag, wiecej)) continue;

        int nie_mam = lmian+1;
        while((nie_mam-1)*nie_wyszlo.se >= nie_wyszlo.fi*mian) --nie_mam;
        int mniej = nie_mam-1;

        for(int poc = wiecej, kon = mniej; poc <= kon;){
            int sr = (poc+kon)/2;
            if(xd(ciag, sr)){
                pii tmp = {sr, mian};
                if(tmp.fi*wyn.se > wyn.fi*tmp.se) wyn = tmp;
                poc = sr+1;
            }
            else{
                pii tmp = {sr, mian};
                if(tmp.fi*nie_wyszlo.se < nie_wyszlo.fi*tmp.se) nie_wyszlo = tmp;
                kon = sr-1;
            }
        }
    }
    printf("%d/%d\n", wyn.fi, wyn.se);
}

int main(){
    //ios_base::sync_with_stdio(0);
    //cin.tie(0);
    int tt = 1;
    //tt = I();
    while(tt--) answer();
}