#include <bits/stdc++.h>

using namespace std;

int main(){
	int n;
	cin >> n;
	string s;
	cin >> s;
	s = "." + s;
	int ans = 0;
	for(int i = 3; i <= n; i++) {
		int cnt = (s[i - 2] == '0') + (s[i - 1] == '0') + (s[i] == '0');
		if (cnt == 3) {
			s[i - 1] = '1';
			s[i] = '1';
			ans += 2;
		}
		else if (cnt == 2) {
			if (s[i] == '0') {
				s[i] = '1';
				ans++;
			}
			else if (s[i - 1] == '0') {
				s[i - 1] = '1';
				ans++;
			}
		}
	}
	cout << ans;
}