#include <iostream>
#include <fstream>
using namespace std;
ifstream f("medie.in");
ofstream g("medie.out");
int n,i,j,m,a[7003],S;
int main()
{
    f>>n;
    for(;n>0;--n)
    {
        f>>i;
        ++a[i];
    }
    S=0;
    for(m=1;m<=6;++m)
    {
        S+=a[m]*(a[m]-1)*(a[m]-2)/2;
        i=m-1;j=m+1;
        while(i>0&&j<7001)
        {
            S+=a[m]*a[i]*a[j];

            --i;++j;
        }

    }
    g<<S;
}