#include <iostream>
#include <fstream>
#include <algorithm>


using namespace std;
ifstream in("nrtri.in");
ofstream out("nrtri.out");
int frec[30010];
int v[8010];

int j=0,mem=0;
int sol=0;
int caut(int poz,int val)
{   
	if(v[poz]<val)return 0;
	sol++;
	if(poz==0)return 0;
	caut (poz-1,val);
	
	return 0;
	
}






int main()
{

int n,x,i,k;

in>>n;
for(i=0;i<n;i++)
	in>>v[i];
sort(v,v+n);

for(i=n-1;i>1;i--)
	for(j=i-1;v[j]>=v[i]/2&&j>0;j--)
		caut(j-1,v[i]-v[j]);


		
	

out<<sol;


return 0;
        
  
  
  
  
  
}