#include <bits/stdc++.h>

using namespace std;
ifstream f("medie.in");
ofstream g("medie.out");
int n,x,fr[14005],i,maxim,j;
long long sum;
int main()
{
    f>>n;
    for (i=1;i<=n;i++)
    {
        f>>x;
        fr[x]++;
        maxim=max(maxim,x);
    }
    for (i=1;i<=maxim;i++)
    {
        sum=sum+(fr[i]*(fr[i]-1)*(fr[i]-2))/2;
        for (j=1;j<=i-1;j++)
        {
            sum=sum+fr[i-j]*fr[i+j]*fr[i];
        }
    }
    g<<sum;
    return 0;
}