#include<iostream>
using namespace std;
int abacus(int *pointer,int n);
int main()
{
	int n,i,a[100];
	cin>>n;
	for(i=0;i<n;i++)
	{
		cin>>a[i];
	}
	cout<<abacus(a,n);
} 
int abacus(int *pointer,int n)
{
	int i,j,count=0,k;
	for(i=0;i<n;i++)
	{
		for(j=0;j<n;j++)
		{
			for(k=0;k<n;k++)
			{
				if(*(pointer+i)==*(pointer+j)+*(pointer+k)&&j!=k)
				count++
			}
		}
	}
	return count/2;
}