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