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

int INF = 1e8;

template <typename T>
bool chmax(T &a, const T& b) {
    if (a < b) {
        a = b;  // aをbで更新
        return true;
    }
    return false;
}

template <typename T>
bool chmin(T &a, const T& b) {
    if (a > b) {
        a = b;  // aをbで更新
        return true;
    }
    return false;
}
int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int N; string S;
    cin >> N >> S;

    vector<int> distances(N, INF);
    int prev = -INF;
    for (int i = 0; i < N; i++) {
        if (S[i] == '#') prev = i;
        chmin(distances[i], i - prev);
    }

    prev = INF;
    for (int i = N - 1; i >= 0; i--) {
        if (S[i] == '#') prev = i;
        chmin(distances[i], prev - i);
    }

    int answer = -INF;
    int max_dist = 0;

    for (int i = 0; i < N; i++) {
        if (chmax(max_dist, distances[i])) {
            answer = i + 1;
        }
    }

    cout << answer << '\n';
}