#include <bits/stdc++.h>
using namespace std;
int mx[4] = {0, 0, 1, -1};
int my[4] = {-1, 1, 0, 0};
int n, m, cnt, cou;
char a[55][55];
bool used[55][55];
bool good(int x, int y) { return (x >= 0 && x < n && y >= 0 && y < m); }
void dfs(int i, int j) {
  used[i][j] = true;
  cou++;
  for (int k = 0; k < 4; k++)
    if (good(i + mx[k], j + my[k]) && a[i + mx[k]][j + my[k]] == '#' &&
        !used[i + mx[k]][j + my[k]])
      dfs(i + mx[k], j + my[k]);
}
int main() {
  scanf("%d%d\n", &n, &m);
  for (int i = 0; i < n; i++) {
    scanf("%s\n", &a[i]);
    for (int j = 0; j < m; j++)
      if (a[i][j] == '#') cnt++;
  }
  if (cnt <= 2)
    printf("-1\n");
  else {
    int ans = 2;
    for (int i = 0; i < n; i++)
      for (int j = 0; j < m; j++)
        if (a[i][j] == '#') {
          a[i][j] = '.';
          cou = 0;
          memset(used, 0, sizeof(used));
          for (int si = 0; si < n; si++)
            for (int sj = 0; sj < m; sj++)
              if (a[si][sj] == '#') dfs(si, sj), si = n, sj = m;
          if (cou != cnt - 1) ans = 1;
          a[i][j] = '#';
        }
    printf("%d\n", ans);
  }
  return 0;
}
