import java.util.*;

public class Solution {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int c[] = new int[n];
        for(int i=0; i < n; i++){
            c[i] = in.nextInt();
        }
        int count = -1;
        for (int i = 0; i < n; i++, count++) {
            if (i<n-2 && c[i+2]==0) i++;
        }
        System.out.println(count);
    }
}

def jumpingOnClouds(c):
    if len(c) == 1 : return 0
    if len(c) == 2: return 0 if c[1]==1 else 1
    if c[2]==1: 
        return 1 + jumpingOnClouds(c[1:])
    if c[2]==0:
        return 1 + jumpingOnClouds(c[2:])

int count = 0;
for (int i = 0; i < n - 1; i++) {
    if (c[i] == 0) i++;
    count++;
}
System.out.println(count);

        var jumps = 0;
        for(int i=0; i<n-1; i++, jumps++)
            if (i+2 < n && c[i+2] == 0)
                i++;
        
        Console.WriteLine(jumps);