#include<stdio.h>
int n,i,j,k,f[7001],nr,sol;
int main()
{
    freopen("medie.in","r",stdin);
    freopen("medie.out","w",stdout);
    scanf("%d",&n);
    for(i=1;i<=n;i++)
    {
        scanf("%d",&nr);
        f[nr]++;
        if(nr>k)
            k=nr;
    }
    for(i=1;i<=k;i++)
    {
        for(j=i+1;j<=k;j++)
        {
            if((i+j)%2==0)
            sol+=f[i]*f[j]*f[(i+j)/2];
        }
        sol+=f[i]*(f[i]-1)*(f[i]-2)/2;
    }
    printf("%d",sol);
    return 0;

}