import java.util.Scanner;

/**
 * Created by Alexandru on 2/16/2015.
 */
public class prog {

    public static int a, n, l, nr;

    public static void main (String[] args)
    {
        Scanner s= new Scanner(System.in);
        n= s.nextInt();
        a=0;
        for(int i=1;i<=n;i++)
        {
            l=s.nextInt();
            if(a==1 && l==1) {
                nr++;
                l = 0;
            }
            a=l;
        }

        System.out.print(nr);
        System.out.print('\n');


    }

}