#include <bits/stdc++.h>
using namespace std;
int getLastBlackWithoutWhiteIndex(string s) {
  for (int i = s.size() - 1; 0 <= i; --i) {
    if (s[i] == '.') {
      return i;
    }
  }
  return 0;
}
int main() {
  int n;
  string s;
  cin >> n >> s;
  int c = getLastBlackWithoutWhiteIndex(s);
  int b, w;
  for (int i = b = w = 0; i <= c; ++i) {
    if (s[i] == '#')
      ++b;
    else
      ++w;
  }
  cout << min(w, b) << endl;
}
