#include <stdio.h>
#include <algorithm>

using namespace std;

int v[900],i,j,n,nr;

int main()
{
	freopen("nrtri.in","r",stdin);
	freopen("nrtri.out","w",stdout);
	
	scanf("%d", &n);
	for (i=1;i<=n;++i)
		 scanf("%d", &v[i]);
	sort(v+1,v+n+1);
	for (i=1;i<=n;++i)
		 for (j=1;j<=i;++j)
			  if (binary_search(v+1,v+n+1,v[i]+v[j]))
		           nr++;
	printf("%d",nr);
return 0;
}