#include <iostream>
#include <fstream>
using namespace std;

int main() {
    int N, ans;
    string S;
    cin >> N >> S;
    ans = 0;
    if(N == 1){
        cout << ans << endl;
        return 0;
    }
    if(S[0] == '0' && S[1] == '0'){
        ans++;
        S[1] = '1';
    }
    for(int i = 2; i < N; i++){
        if(S[i] == '0'){
            if(S[i-1] == '0' || S[i-2] == '0'){
                ans++;
                S[i] = '1';
            }
        }
    }
    cout << ans << '\n';
    return 0;
}