import java.util.Scanner;

public class Main {
	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		char[] s = sc.next().toCharArray();
		sc.close();

		int ans = 0;
		for (int i = 1; i < n; i++) {
			if (s[i - 1] == '0' && s[i] == '0') {
				ans++;
				s[i] = '1';
			}
			if (i >= 2 && s[i - 2] == '0' && s[i - 1] == '1' && s[i] == '0') {
				ans++;
				s[i] = '1';
			}
		}
		System.out.println(ans);
	}
}