#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;

    string t = s;
    int rr;

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

    for (int u = 0; u < 2; u++) {
        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;
            }
        }

        if (u == 0) {
            rr = r;
        } else {
            rr = min(rr, r);
            break;
        }

        s = t;
        reverse(s.begin(), s.end());
        k = n - 1 - k;
    }

    cout << rr << endl;

    return 0;
}