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

int main() {
	int N;
	cin >> N;
	string S;
	cin >> S;
	
	set<int> s = {-1000000, 1000000};
	for(int i = 0; i < N; ++i) if(S[i] == '#') s.insert(i);
	
	int maxd = 0, ans = -1;
	for(int i = 0; i < N; ++i) if(S[i] == '.') {
		auto it = s.upper_bound(i);
		int d = min(*it - i, i - *prev(it));
		if(maxd < d) maxd = d, ans = i;
	}
	
	cout << ans + 1 << "\n";
}