#include <bits/stdc++.h>

using namespace std;

const int INF = 1 << 30;

int solve(string S, int N)
{
  int right = N, ret = 0;
  for(int i = N; i >= 0; i--) {
    if(S[i] == '#') right = i;
  }
  for(int i = N - 1; i >= right; i--) {
    S[i] = ".#"[S[i] == '.'];
    ++ret;
  }
  S += ".";
  int rest = count(begin(S), end(S), '#');
  while(rest > 0) {
    ++right;
    ++ret;
    S[right] = ".#"[S[right] == '.'];
    if(S[right] == '.') rest--;
    else rest++;
    if(S[right - 1] == '#') {
      --right;
      ++ret;
      S[right] = ".#"[S[right] == '.'];
      if(S[right] == '.') rest--;
      else rest++;
    }
  }
  return (ret);
}

int main()
{
  int N;
  string S, T;
  cin >> N;
  cin >> S;
  T = S;
  reverse(begin(T), end(T));
  cout << min(solve(S, N - 1), solve(T, (int) S.size() - N)) << endl;
}