import java.util.Arrays;
import java.util.Scanner;

public class Main implements Runnable {
    public static void main(String[] args) {
        new Thread(null, new Main(), "", 512 * 1024 * 1024).start();
    }
    
    public void run() {
    	Scanner sc=new Scanner(System.in);
    	int n=sc.nextInt();
    	char[]cs=sc.next().toCharArray();
    	int pre=-10;
    	int ans=0;
    	for(int i=0;i<n;++i) {
    		if(cs[i]=='0') {
    			if(i-pre<=2) {
    				++ans;
    			} else {
    				pre=i;
    			}
    		}
    	}
    	System.out.println(ans);
    }
    
    void tr(Object...objects) {System.out.println(Arrays.deepToString(objects));}
}