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

int main() {
    int N;
    string S;
    cin >> N >> S;
    
    int res = 0;
    for (int i = 0; i < N; ) {
        if (S[i] == '0') {
            int j = i;
            while (j < N && S[j] == '0') {
                j++;
            }
            int len = j - i;
            res += len / 2;
            i = j;
        } else {
            i++;
        }
    }
    cout << res << endl;
    return 0;
}