// numarare triunghiuri.cpp : Defines the entry point for the console application.
//
//#include "stdafx.h"
#include "fstream"
#include "algorithm"
using namespace std;
int n;
int main()
{
	ifstream f("nrtri.in");
	ofstream g("nrtri.out");
	f>>n;
	int i;
	int a[800];
	for(i=0;i<n;i++)
		f>>a[i];
	sort(a,a+n);
	int j;
	int nr=0;
	for(i=0;i<n-2;i++)
		for(j=i+1;j<n-1;j++)
		{
			int p,u,m,x;
			p=j+1;
			u=n-1;
			m=(p+u)/2;
			x=a[i]+a[j];
			while(p<=u)
			{
				m=(p+u)/2;
				if(a[p]>x)
					break;
				if(a[m]>x)
					u=m-1;
				if(a[m]<x)
					p=m+1;
				if(a[m]==x)
				{
					nr+=m-j;
					break;
				}
				if((a[m]<=x)&&(a[m+1]>x))
				{
					nr+=m-j;
					break;
				}
				if((a[m]<=x)&&(m==n-1))
				{
					nr+=m-j;
					break;
				}
			}
		}
	g<<nr;
	return 0;
}