#include <stdio.h>

int v[7001],i,j,n,x,sol;

int main()
{
    freopen("medie.in","r",stdin);
    freopen("medie.out","w",stdout);
    scanf("%d",&n);
    for (i=1;i<=n;++i)
    {
        scanf("%d",&x);
        ++v[x];
    }
    for (i=1;i<7000;++i)
    {
        for (j=i+2;j<7001;j+=2)
            sol+=v[i]*v[j]*v[(i+j)/2];
        sol+=v[i]*(v[i]-1)*(v[i]-2)/2;
    }
    printf("%d",sol);
    return 0;
}