#include<fstream.h>

float v[9009];
long long n;

void citire()
{
  ifstream in("medie.in");
  in>>n;
  for (long long i=1; i<=n; i++)
    in>>v[i];
  in.close();
}

void calcul()
{
  long long contor=0, i, j, k;
  for (i=1; i<=n; i++)
    for (k=2; k<=n; k++)
      for (j=1; j<k; j++)
	{
	  if ((v[j]+v[k])/2==v[i] && i!=j && i!=k)
	    contor++;
	}
  ofstream out("medie.out");
  out<<contor;
  out.close();
}

int main()
{
  citire();
  calcul();
  return 0;
}