#include <iostream>
#include<fstream>
using namespace std;
long long rasp;
int i,n,ap[7005],j,x;
int main()
{
    ifstream f("medie.in");
    ofstream g("medie.out");
    f>>n;
    for(i=1;i<=n;i++)
        {f>>x;ap[x]++;}
    for(i=1;i<=7000;i++)
    {
        rasp+=ap[i]*(ap[i]-1)*(ap[i]-2)/2;
        for(j=1;j<=min(i,7000-i);j++)
            rasp+=ap[i]*(ap[i-j]*ap[i+j]);
    }
    g<<rasp;
    return 0;
}