#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, a, b;
  char inpu;
  a = 0;
  b = 0;
  cin >> n;
  for (int x = 0; x < n; x++) {
    cin >> inpu;
    if (inpu == '#')
      a++;
    else
      b++;
  }
  if (a > b)
    cout << b;
  else
    cout << a;
}
