#include<bits/stdc++.h>
using namespace std;
int a[101];
int main()
{
	int n,i,count=0,sum,k,j;
	cin>>n;
	for(i=1;i<=n;++i)
	{
		cin>>a[i];
	}

	for(i=1;i<=n-1;++i)
	{
		for(k=i+1;k<=n;++k)
		if(a[i]!=a[k])
		{
			for(j=1;j<=n;++j)		
		{
			if(a[j]==a[i]+a[k])
				{
					count++;
					break;
				}
		}
		}
	}
	cout<<count;
	return 0;
}