#include <algorithm>
#include <fstream>
using namespace std;
int v[9005];
int main()
{   ifstream f("medie.in");
    ofstream g("medie.out");

    int n, i, j, h, cont=0;
    f>>n;
    for (i=1;i<=n;++i)
        f>>v[i];
    for (i=1;i<=n;++i)
    {   j=1;
        while (j<=n)
        {   h=j+1;
            if(j!=i)
              while (h<=n)
              { if (h!=j && h!=i)
                  if (v[i]==(v[j]+v[h])/2 && (v[j]+v[h])%2==0)
                    cont++;
                 ++h;
              }
            ++j;
        }
    }
    g<<cont;

    return 0;
}