#include<fstream.h>
int main()
{int n,l,v[7000],k,i,j;
ifstream f("medie.in");
ofstream g("medie.out");
f>>n;l=0;
for(i=1;i<=n;i++)f>>v[i];
for(i=1;i<=n;i++)
	for(j=1;j<=n;j++)
		for(k=1;k<=n;k++)if(i!=j&&i!=k&&j<k)if(v[i]=(v[j]+v[k])/2)l++;
g<<l;
f.close ();
g.close ();
return 0;
}