#include <iostream>
#include <fstream>

using namespace std;
ifstream fin("medie.in");
ofstream fout("medie.out");

long long n,i,j,k,rez,v[900005],f[700005];

int main() {
	
	fin>>n;
	for(i=1;i<=n;i++)
	{
		fin>>v[i];
		f[v[i]]++;
	}
	f[v[1]]--;
	for(i=2;i<n;i++)
	{
		f[v[i]]--;
		for(j=1;j<i;j++)
		{
			k=2*v[i]-v[j];
			rez+=f[k];
		}
	}
	fout<<rez*3<<"\n";
}