#include <bits/stdc++.h>
using namespace std;

int main()
{
    int N;
    cin >> N;
    string S;
    cin >> S;
    int ans = 0;
    for (int i = 0; i < N - 1; i++)
    {
        if (S[i] == '0' && S[i + 1] == '0')
        {
            S[i + 1] = '1';
            ans++;
        }
    }
    for (int i = 0; i < N - 2; i++)
    {
        if (S[i] == '0' && S[i + 1] == '1' && S[i + 2] == '0')
        {
            ans++;
            S[i + 2] = '1';
        }
    }

    cout << ans;
}