#include<iostream.h>
#include<fstream.h>

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

int main ()
{
	int i,j,k,n,V[9000],c=0,ok=1,aux;
	
	f>>n;
	for(i=0;i<n;i++)f>>V[i];
	
	while(ok)
	{
		ok=0;
		for(i=0;i<n-1;i++)
			if(V[i]>V[i+1])
			{
				aux=V[i];
				V[i]=V[i+1];
				V[i+1]=aux;
				ok=1;
			}
	}
	 
	//for(i=0;i<n;i++)g<<V[i]<<" ";
	
	int endj, startk;
	
	for(i=0;i<n;i++)
	{	
		//cout <<i<< "=i\n";
		endj=i;
		if (endj<n-1) while (V[endj+1]==V[i]&&endj<n-1) endj++;
		//cout <<endj<< "=endj\n";
		for(j=0;j<endj;j++)
		{
			//cout <<j<< "=j\n";
			startk=i+1;
			if (i>0&&V[i-1]==V[i])
			{
			startk=i-1;	
			if (startk>0) while(V[startk-1]==V[i]) startk--;
			}
			//cout <<startk<< "=startk\n";
			for(k=startk;k<n;k++) 
				if(V[i]*2==V[j]+V[k]&&i!=k&&i!=j&&j!=k&&j<k) 
					{
						//cout << "("<<i<<","<<j<<","<<k<<")\n";
						c++;
					}
	
		}	
	}	
    g<<c;
	f.close();
	g.close();
	return 0;
}