#include <bits/stdc++.h>
using namespace std;
const int N = 60;
int n, m;
char s[N][N];
bool vis[N][N];
int tmp;
int dx[] = {-1, 0, 1, 0};
int dy[] = {0, -1, 0, 1};
inline bool in(int x, int y) { return x >= 0 && x < n && y >= 0 && y < m; }
void dfs(int x, int y) {
  vis[x][y] = 1;
  tmp++;
  for (int i = 0; i < 4; ++i) {
    int tx = x + dx[i];
    int ty = y + dy[i];
    if (in(tx, ty) && s[tx][ty] == '#') {
      if (!vis[tx][ty]) {
        dfs(tx, ty);
      }
    }
  }
}
int main() {
  scanf("%d%d", &n, &m);
  for (int i = 0; i < n; ++i) {
    scanf("%s", s[i]);
  }
  int cnt = 0;
  for (int i = 0; i < n; ++i) {
    for (int j = 0; j < m; ++j) {
      if (s[i][j] == '#') {
        ++cnt;
      }
    }
  }
  if (cnt == 1 || cnt == 2) {
    printf("-1\n");
    return 0;
  }
  for (int i = 0; i < n; ++i) {
    for (int j = 0; j < m; ++j) {
      if (s[i][j] == '#') {
        s[i][j] = '.';
        memset(vis, 0, sizeof(vis));
        for (int a = 0; a < n; ++a) {
          for (int b = 0; b < m; ++b) {
            if (s[a][b] == '#') {
              tmp = 0;
              dfs(a, b);
              if (tmp != cnt - 1) {
                printf("1\n");
                return 0;
              }
              a = n, b = m;
            }
          }
        }
        s[i][j] = '#';
      }
    }
  }
  printf("2\n");
  return 0;
}
