#include <bits/stdc++.h>
using namespace std;

int main() {
	int n;
	string s;
	cin >> n >> s;
	vector<int> distance(n);
	int dist = 10000000;
	for(int i = 0; i < n; i++){
		if(s[i] == '#'){
			dist = 0;
			distance[i] = -1;
		} else {
			dist++;
			distance[i] = dist;
		}
	}
	dist = 10000000;
	for(int i = n - 1; i >= 0; i--){
		if(s[i] == '#'){
			dist = 0;
			distance[i] = -1;
		} else {
			dist++;
			distance[i] = min(distance[i], dist);
		}
	}
	int max_distance = 0;
	int max_i;
	for(int i = 0; i < n; i++){
		if(max_distance < distance[i]){
			max_distance = distance[i];
			max_i = i;
		}
	}
	cout << max_i + 1 << endl;
}