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

int main() {
    int N;
    string S;
    cin >> N >> S;
    int ans = 0,sum = 0;
    reverse(S.begin(),S.end());
    for(int i = 0; i < N; i++) {
        if(S[i] == '#') {
            ans = max(ans,i+1+sum);
            sum++;
        }
        else {
            sum--;
        }
        sum = max(sum,0);
    }
    cout << ans << endl;
}