/* -*- coding: utf-8 -*-
 *
 * 3745.cc:  No.3745 Line Seats - yukicoder
 */

#include<cstdio>
#include<algorithm>

using namespace std;

/* constant */

const int MAX_N = 100000;
const int INF = 1 << 30;

/* typedef */

/* global variables */

char s[MAX_N + 4];
int ls[MAX_N + 1], rs[MAX_N + 1];

/* subroutines */

/* main */

int main() {
  int n;
  scanf("%d%s", &n, s);

  ls[0] = INF;
  for (int i = 0; i < n; i++)
    ls[i + 1] = (s[i] == '#') ? 0 : ls[i] + 1;
  rs[n] = INF;
  for (int i = n - 1; i >= 0; i--)
    rs[i] = (s[i] == '#') ? 0 : rs[i + 1] + 1;

  int maxd = 0, maxi = -1;
  for (int i = 0; i < n; i++)
    if (s[i] == '.') {
      int d = min(ls[i + 1], rs[i]);
      if (maxd < d) maxd = d, maxi = i;
    }

  printf("%d\n", maxi + 1);
  
  return 0;
}