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