#include <bits/stdc++.h>
using namespace std;
int main() {
  int N;
  string S;
  cin >> N >> S;
  int w = 0, b = 0;
  for (int i = 0; i < N; ++i) {
    if (S[i] == '.') {
      w++;
    } else if (S[i] == '#') {
      b++;
    }
  }
  cout << min(w, b) << endl;
  return 0;
}
