#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  char s[n];
  for (int i = 0; i < n; i++) cin >> s[i];
  int ans = 0;
  int white = 0;
  int black = 0;
  for (int i = 0; i < n; i++) {
    if (s[i] == '#')
      black++;
    else
      white++;
  }
  if (black > white)
    ans = white;
  else
    ans = black;
  cout << ans << endl;
  return 0;
}
