#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <cmath>
using namespace std;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);

    int k;
    cin >> k;
    k--;

    string s;
    cin >> s;

    int n = (int)s.size();

    int r = 0, c = 0;

    for (int i = 0; i < n; i++) {
        s[i] = s[i] == '#';
        c += s[i];
    }

    int i0 = k;
    for (int i = 0; i < k; i++) {
        if (s[i] != 0) {
            for (int j = i; j < k; j++) {
                r++;
                c -= s[j];
                s[j] ^= 1;
                c += s[j];
            }
            i0 = i;
            break;
        }
    }

    for (int i = i0; i < n; i++) {
        //for (int i = 0; i < n; i++) {
        //    cout << ".#"[s[i]];
        //}
        //cout << ' ' << c << ' ' << r << endl;
        if (c == 0) break;
        if (s[i] == 0) {
            r++;
            c -= s[i + 1];
            s[i + 1] ^= 1;
            c += s[i + 1];
        } else if (c == 2 && s[i] && s[i + 1]) {
            r += 2;
            c -= 2;
            s[i] = 0;
            s[i + 1] = 0;
        } else {
            r += 3;
            c--;
            s[i] = 0;
        }
    }

    cout << r << endl;

    return 0;
}