#include <vector>
#include <string>
#include <cstring>
#include <queue>
#include <iostream>
#include <fstream>
#include <algorithm>
#include <cmath>

using namespace std;

int nextInt() {
    int x;
    scanf("%d", &x);
    return x;
}

char inp[10000];
string nextString() {
    scanf("%s", inp);
    return inp;
}

double nextDouble() {
    double x;
    scanf("%lf", &x);
    return x;
}

char a[30][30];

int p[1 << 25];
char h[1 << 25];
int hMask[25];
char bits[1 << 25];

int main() {
    int n = nextInt();
    int m = nextInt();

    if (n == 0 || m == 0) {
        printf("0\n");
        return 0;
    }

    for (int i = 0; i < n; ++i) {
        scanf("%s", a[i]);
    }

    for (int j = 0; j < m; ++j) {
        h[1 << j] = j;
        for (int i = 0; i < n; ++i) {
            if (a[i][j] == '*') {
                hMask[j] |= 1 << i;
            }
        }
    }
    bits[0] = 0;
    for (int i = 1; i < (1 << 25); ++i) {
        bits[i] = bits[i & (i - 1)] + 1;
    }

    p[(1 << m) - 1] = 0;
    int res = m;
    for (int mask = (1 << m) - 2; mask >= 0; --mask) {
        int m2 = mask | (mask + 1);
        p[mask] = p[m2] | hMask[h[m2 - mask]];
        int t = bits[mask] > bits[p[mask]] ? bits[mask] : bits[p[mask]];
        if (res > t) {
            res = t;
        }
    }
    printf("%d\n", res);

    return 0;
}