#include <bits/stdc++.h>
using namespace std;
int main() {
  long N;
  string S;
  cin >> N >> S;
  int color;
  vector<int> vec;
  if (S.at(0) == '.') {
    color = 0;
  } else {
    color = 1;
  }
  for (int i = 1; i < N; i++) {
    if (S.at(i) != S.at(i - 1)) {
      vec.push_back(i);
    }
  }
  int minimum = N;
  if (vec.size() == 0) {
    minimum = 0;
  } else if (color == 0) {
    for (int i = 0; i < vec.size(); i += 2) {
      int sum = 0;
      for (int j = 1; j < i; j += 2) {
        sum += (vec.at(j) - vec.at(j - 1));
      }
      for (int k = i + 2; k < vec.size(); k += 2) {
        sum += (vec.at(k) - vec.at(k - 1));
      }
      if (vec.size() % 2 == 0) {
        sum += (N - vec.at(vec.size() - 1));
      }
      minimum = min(minimum, sum);
    }
  } else if (color == 1) {
    for (int i = 1; i < vec.size(); i += 2) {
      int sum = 0;
      sum += vec.at(0);
      for (int j = 1; j < i; j += 2) {
        sum += (vec.at(j) - vec.at(j - 1));
      }
      for (int k = i + 2; k < vec.size(); k += 2) {
        sum += (vec.at(k) - vec.at(k - 1));
      }
      if (vec.size() % 2 == 1) {
        sum += (N - vec.at(vec.size() - 1));
      }
      minimum = min(minimum, sum);
    }
  }
  cout << minimum << endl;
}
