#include<fstream>
#include<iostream>
#include<vector>
using namespace std;
int a[7012];
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[x]++;
        if (x>maxim)
            maxim=x;
    }
 
    for (i=1;i<=maxim;i++)
    {
        for (j=i+2;j<=maxim;j=j+2)
            perechi+=a[i]*a[j]*a[(i+j)/2];
        perechi+=(a[i]-1)*a[i]*(a[i]-2)/2;
    }
    fprintf(g,"%d",perechi);
}