#include <cstdio>
#include <cstring>
#include <vector>
#include <algorithm>

const int N = 1e6 + 10, inf = 1e9;

char s[N];
int a[N];

int solve(char s[], int n, int p) {
  for (int i = 0; i < n; ++i) a[i] = s[i] == '.';
  int l = 0, r = n - 1;
  while (r >= 0 && a[r]) --r;
  while (l < n && a[l]) ++l;
  if (l > r) return 0;
  if (r < p) return inf;
  int cur = 0;
  for (int i = 0; i < n; ++i) {
    if (l < i && i <= r) a[i] = !a[i], ++cur;
    if ((l <= i && i < p) || (p < i && i <= l)) a[i] = !a[i], ++cur;
  }
  std::vector<int> dq;
  for (int i = 0; i < n; ++i) {
    if (!a[i]) dq.emplace_back(i);
  }
  for (size_t i = 0; i + 1 < dq.size(); i += 2) {
    int u = dq[i], v = dq[i + 1];
    cur += (v - u) * 2;
  }
  if (dq.size() & 1) cur += std::abs(r - 1 - dq.back()) * 2 + 1;
  return cur;
}

int main() {
  int T = 1;
  //scanf("%d", &T);
  for (int cas = 1; cas <= T; ++cas) {
    int p;
    scanf("%d%s", &p, s);
    int n = strlen(s);
    std::vector<int> steps(n);
    for (int i = p; i <= p; ++i) {
      steps[i] = solve(s, n, i);
    }
    std::reverse(s, s + n);
    for (int i = n - 1 - p; i <= n - 1 - p; ++i) {
      steps[n - 1 - i] = std::min(steps[n - 1 - i], solve(s, n, i));
    }
    printf("%d\n", steps[p]);
  }
  return 0;
}