#include<stdio.h>


void citire(int &n,int v[])
{ int i;

 FILE*f=fopen("medie.in", "r");

 fscanf(f, "%d", &n);
 for(i=1;i<=n;i++)
     fscanf(f, "%d", &v[i]);

 fclose(f);

 }


 int medie(int a, int b, int c)
 {float S=b+c,m;

  m=(float)S/2;
  if(a==m) return 1;
  else return 0;
  
  }

  int main()
  {int n,v[9100],i,j,k,x=0;

   FILE*g=fopen("medie.out", "w");
   citire(n, v);

   for(i=1;i<=n;i++)
      for(j=i+1;j<=n;j++)
	 for(k=j+1;k<=n;k++)
	      { if(medie(v[i],v[j],v[k])==1) x++;
	        if(medie(v[j],v[i],v[k])==1) x++;
		if(medie(v[k],v[j],v[i])==1) x++;    
	       }

   fprintf(g, "%d", x);
   fclose(g);

   return 0;
   }