#include <bits/stdc++.h>

using namespace std;

typedef pair<int, int> pii;
typedef pair<long long, int> pli;
typedef pair<int, pair<int, int> > piii;
typedef long long ll;
const int N = 2000086, MOD = 1e9 + 7, INF = 0x3f3f3f3f;
ll res;
int n, m, cnt, w[N];

char s[N];
int main() {
    cin >> n;
    scanf("%s", s + 1);
    int c = 100;
    for (int i = 1; i < n + 1; i++) {
        if (s[i] == '1') c++;
        else {
            if (c >= 2) c = 0;
            else c++, res++;
        }
    }
    printf("%lld\n", res);
    return 0;
}