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