#include <bits/stdc++.h>
using namespace std;
int ans = 0;
int n;
string s;
void mark(int i) {
	s[i] = '1';
	ans++;
}
int main() {
	cin >> n >> s;
	if (n == 1) {
		cout << 0 << endl;
		return 0;
	} else if (n == 2) {
		if (s == "11") cout << 1 << endl;
		else cout << 0 << endl;
		return 0;
	} else {
		for (int i = 0; i < (int)s.length() - 2; i++) {
			string t = s.substr(i,3);
			// cerr << t << endl;
			if (t == "000") {
				mark(i+1); mark(i+2);
			} else if (t == "001") {
				mark(i+1);
			} else if (t == "010") {
				mark(i+2);
			} else if (t == "100") {
				mark(i+2);
			} else {
				// more than 2 1s, fine
			}
		}
		cout << ans << endl;
	}
}