#include <bits/stdc++.h>   using namespace std;   char a[1001][1001];   int vis[1001][1001];   int n, m;   void dfs(int x, int y) {     vis[x][y] = 1;     if (x - 1 >= 0 && !vis[x - 1][y] && a[x - 1][y] ==  # ) {       dfs(x - 1, y);     }     if (x + 1 < n && !vis[x + 1][y] && a[x + 1][y] ==  # ) {       dfs(x + 1, y);     }     if (y - 1 >= 0 && !vis[x][y - 1] && a[x][y - 1] ==  # ) {       dfs(x, y - 1);     }     if (y + 1 < m && !vis[x][y + 1] && a[x][y + 1] ==  # ) {       dfs(x, y + 1);     }   }   int main() {     ios_base::sync_with_stdio(false);     cin.tie(NULL);     cout.tie(NULL);     cin >> n >> m;     int f1 = 0, f2 = 0, f3 = 0;     int awr = 0, awc = 0, c = 0, ans = 0;     for (int i = 0; i < n; ++i) {       cin >> a[i];     }     for (int i = 0; i < n; ++i) {       for (int j = 0; j < m; ++j) {         if (!f1 && a[i][j] ==  # ) {           f1 = 1;         } else if (f1 && !f2 && a[i][j] ==  . ) {           f2 = 1;         } else if (f1 && f2 && !f3 && a[i][j] ==  # ) {           f3 = 1;         }       }       if (f1 && f2 && f3) {         cout <<  -1 n ;         goto here;       } else {         f1 = f2 = f3 = 0;       }     }     for (int j = 0; j < m; ++j) {       for (int i = 0; i < n; ++i) {         if (!f1 && a[i][j] ==  # ) {           f1 = 1;         } else if (f1 && !f2 && a[i][j] ==  . ) {           f2 = 1;         } else if (f1 && f2 && !f3 && a[i][j] ==  # ) {           f3 = 1;         }       }       if (f1 && f2 && f3) {         cout <<  -1 n ;         goto here;       } else {         f1 = f2 = f3 = 0;       }     }     for (int i = 0; i < n; ++i) {       c = 0;       for (int j = 0; j < m; ++j) {         if (a[i][j] ==  . ) {           c++;         }       }       if (c == m) {         awr = 1;         break;       }     }     for (int j = 0; j < m; ++j) {       c = 0;       for (int i = 0; i < n; ++i) {         if (a[i][j] ==  . ) {           c++;         }       }       if (c == n) {         awc = 1;         break;       }     }     if (awr ^ awc) {       cout <<  -1 n ;       goto here;     }     for (int i = 0; i < n; ++i) {       for (int j = 0; j < m; ++j) {         if (a[i][j] ==  #  && !vis[i][j]) {           ans++;           dfs(i, j);         }       }     }     cout << ans <<   n ;   here:;   }   