#include <iostream>
#include <iomanip>
#include <cstring>
#include <algorithm> 
#include <math.h>
#include <queue>
#include <functional>
#include <map>
#include <vector>
#include <string>
using namespace std;
typedef long long ll;

int n;
int S[1000005], T[1000005];
string s;
int main(void){
    cin >> n >> s;
    S[0] = S[s.size() + 1] = 0;
    for (int i = 1; i <= s.size(); i++){
        T[i] = 0;
        if (s[i - 1] == '.') S[i] = 0;
        else S[i] = 1;
    }

    int start[2] = { n, n };

    for (int i = 1; i <= n; i++){
        if (T[i] == S[i]) continue;
        start[0] = i;
        break;
    }

    for (int i = s.size(); i >= n; i--){
        if (T[i] == S[i]) continue;
        start[1] = i;
        break;
    }

    int id;
    if (n - start[0] < start[1] - n) id = start[0];
    else id = start[1];

    ll ans = 0;
    for (int i = id; i < n; i++){
        T[i] = (T[i] + 1) % 2;
        ans++;
    }
    for (int i = id; i > n; i--){
        T[i] = (T[i] + 1) % 2;
        ans++;
    }

    if (id < n || (id == n&&start[1] != n)){
        while (T[start[1]] != S[start[1]]){
            if (T[id] == S[id]){
                T[id + 1] = (T[id + 1] + 1) % 2;
                ans++;
                id++;
                continue;
            }
            T[id + 1] = (T[id + 1] + 1) % 2;
            T[id] = (T[id] + 1) % 2;
            ans += 2;
            id++;
        }
    }
    else if (id>n || (id == n&&start[0] != n)){
        while (T[start[0]] != S[start[0]]){
            if (T[id] == S[id]){
                T[id - 1] = (T[id - 1] + 1) % 2;
                ans++;
                id--;
                continue;
            }
            T[id - 1] = (T[id - 1] + 1) % 2;
            T[id] = (T[id] + 1) % 2;
            ans += 2;
        }
    }

    cout << ans << endl;
}