# include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 10;
char s[N];
int main() {
	int n;
	scanf("%d%s", &n, s + 1);
	int tot = 0;
	for (int i = 1, x = 0; i <= n; i++) {
		if (s[i] == '1') {
			x = 3;
		}
		if (x) {
			tot++, x--;
		}
	}
	printf("%d", tot);
	return 0;
}