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