#include<fstream>
#include<iostream>
#include<vector>
using namespace std;
vector <int> a(9000);
int maxim, perechi;
int main(void)
{
	int n;
	FILE *f=fopen("medie.in","rt");
	FILE *g=fopen("medie.out","wt");
	fscanf(f,"%d",&n);
	int i,j,x;
	for (i=1;i<=n;i++)
	{
		fscanf(f,"%d",&x);
		a.at(x)++;
		if (x>maxim)
			maxim=x;
	}

	for (i=1;i<=maxim;i++)
	{
		for (j=i+2;j<=maxim;j=j+2)
			perechi+=a.at(i)*a.at(j)*a.at((i+j)/2);
		perechi+=a.at(i)*a.at(j)*a.at((i+j)/2);
	}
	fprintf(g,"%d",perechi);
}