#include <iostream>
#include <algorithm>
#include <vector>
#include <string>

using namespace std;

char flip(char c) {
  return c == '#' ? '.' : '#';
}

int solve(int k, string s) {
  int cnt = 0;

  int left = 0; 
  int right = 0;

  for (int i = 0; i < k; i++) {
    if (s[i] == '#') left++;
  }
  for (int i = k; i < s.size(); i++) {
    if (s[i] == '#') right++;
  }

  while (left + right > 0) {
    if (left > 0) {
      if (k - 1 < 0) return 1e9;
      left -= s[k - 1] == '#';
      k--;
      s[k] = flip(s[k]);
      right += s[k] == '#';
    } else if (right > 0) {
      if (k + 1 >= s.size()) return 1e9;
      right -= s[k] == '#';
      left += s[k] == '#';
      k++;
      right -= s[k] == '#';
      s[k] = flip(s[k]);
      right += s[k] == '#';
    }
    cnt++;
  }

  return cnt;
}

int main() {
  int n;
  cin >> n;
  n--;

  string s;
  cin >> s;

  int ans = solve(n, s);

  n = s.size() - 1 - n;
  reverse(s.begin(), s.end());
  ans = min(ans, solve(n, s));

  cout << ans << endl;
}