#include <fstream.h>

ifstream f("medie.in");
ofstream g("medie.out");

int a[9002],v[7002],n,NrSol;

void citire ()
{ f>>n; 
  for (int i=1; i<=n; i++)
   f>>a[i];
  f.close ();
}

void search ()
{  int i,j,k;
   for (i=1; i<=n; i++)
    for (j=i+1; j<=n; j++)
     for (k=1; k<=n; k++)
      if (a[i]+a[j]=a[k]*2 && k!=j && k!=i) NrSol++;
}

void scrie ()
{ g<<NrSol;
  g.close ();
}

int main ()
{ citire ();
  search ();
  scrie ();
  return 0;
}