#include <stdio.h>
#include <stdlib.h>
int main()
{
    int v[32000],n,i,j,ok=0,l;
    scanf("%d",&n);
    scanf("%d",&v[1]);
    for(i=2;i<=n;i++)
    {
        scanf("%d",&v[i]);
        if(v[i]==v[i-1]&&v[i-1]==1)
        {
            ok++;
            v[i]=0;
        }
    }printf("%d",ok);
    return 0;
}