#include <bits/stdc++.h>
using namespace std;
int main() {
  unsigned long int n, b = 0, w = 0;
  string s;
  cin >> n >> s;
  for (int i = 0; i < n; i++) {
    if (s[i] == '.') w++;
    if (s[i] == '#') b++;
  }
  cout << min(b, w);
}
