#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, blackCount = 0;
  string s;
  cin >> n >> s;
  for (int i = 0; i < n; i++)
    if (s[i] == '#') blackCount++;
  if (blackCount <= n / 2) {
    cout << blackCount << endl;
  } else {
    cout << n - blackCount << endl;
  }
  return 0;
}
