#include <iostream>
#include <vector>
#include <string>
using namespace std;

void out(const vector<bool>& A, int k) {
    for (int i = k - 1; i < A.size(); i++) {
        cout << (A[i] ? 1 : 0);
    }
    cout << endl;
}

void toBitarray(const string& s, vector<bool>& S, int k, int fullN) {
    for (int i = 0; i < k - 1; i++) {
        S[i] = true;
    }

    for (int i = k - 1; i < fullN; i++) {
        S[i] = (s[i - k + 1] == '1') ? true : false;
    }
}

int min_find(const string& s, int N, int n) {
    const int weight_min = (n + 1) / 2;
    const int fullN = N + weight_min - 1;
    int change = 0;
    int H_weight = 0;
    vector<bool> S(fullN);
    vector<bool> K(fullN);

    toBitarray(s, S, weight_min, fullN);

    copy(S.begin(), S.end(), K.begin());

    for (int i = 0; i < n; i++) {
        H_weight = H_weight + (S[i] ? 1 : 0);
    }

    if (H_weight < weight_min) {
        S[n - 1] = true;
        H_weight++;
        change++;
    }

    for (int i = 1; i < fullN - n + 1; i++) {
        H_weight = H_weight - (S[i - 1] ? 1 : 0);
        H_weight = H_weight + (S[i + n - 1] ? 1 : 0);
        if (H_weight < weight_min) {
            S[i + n - 1] = true;
            H_weight++;
            change++;
        }
    }

    return change;
}

int main() {
    int N;
    string s;
    cin >> N >> s;
    cout << min_find(s, N, 3) << endl;
    return 0;
}