import java.util.ArrayList;
import java.util.Scanner;

public class prog {
	public static int panel(ArrayList<Integer> list) {
		int counter = 0;
		for (int i = 0; i < list.size() - 1; i++) {
			if (list.get(i) == list.get(i + 1) && list.get(i) == 1) {
				list.set(i + 1, 0);
				counter++;
			}
		}
	
		return counter;
	}
	
	public static void main(String[] args) {
		Scanner s = new Scanner(System.in);
		ArrayList<Integer> list = new ArrayList<Integer>();
		int n = s.nextInt();
		for (int i = 0; i < n; i++) {
			list.add(s.nextInt());
		}
		
		System.out.println(panel(list));
		
		s.close();		
	}
}