#include <cstdio>

#define VMax 7005

using namespace std;

int N, X[VMax], MaxV, Sum[2*VMax], S;

void Solve ()
{
    for (int i=0; i<MaxV; ++i)
    {
        for (int j=i+1; j<=MaxV; ++j)
        {
            Sum[i+j]+=(X[i]*X[j]);
        }
    }
    for (int i=0; i<=MaxV; ++i)
    {
        S+=(X[i]*Sum[2*i]);
        S+=(X[i]*(X[i]-1)*(X[i]-2)/2);
    }
}

void Read ()
{
    freopen ("medie.in", "r", stdin);
    scanf ("%d", &N);
    for (int i=1; i<=N; ++i)
    {
        int V;
        scanf ("%d", &V);
        ++X[V];
        if (V>MaxV)
        {
            MaxV=V;
        }
    }
}

void Print ()
{
    freopen ("medie.out", "w", stdout);
    printf ("%d\n", S);
}

int main()
{
    Read ();
    Solve ();
    Print ();
    return 0;
}