#include <fstream>
using namespace std;
ifstream fin ("medie.in");
ofstream fout ("medie.out");
int vc[14005];
int main()
{
    int maxi=-1,n,x,i,j;
    long long nr=0;
    fin>>n;
    for (i=1;i<=n;i++)
    {
        fin>>x;
        vc[x]++;
        if (x>maxi)
            maxi=x;
    }
    for (i=1;i<=maxi;i++)
    {
        nr=nr+(vc[i]*(vc[i]-1)*(vc[i]-2))/2;
        for (j=1;j<=i-1;j++)
            nr=nr+vc[i-j]*vc[i+j]*vc[i];
    }
    fout<<nr;
    return 0;
}