#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;
ifstream fin("nrtri.in");
ofstream fout("nrtri.out");
int a[805],n;
int cautbin(int x, int lo, int hi,int j)
{
    int ans=0;
    while(lo<=hi)
    {
        int mid=(lo+hi)/2;
        if(x<a[mid]) hi=mid-1;
        else
        {   if(x<a[mid+1]||mid==n) return mid-j;
            else lo=mid+1;
        }
    }
}
int main()
{
    int sol=0;
    fin>>n;
    for(int i=1;i<=n;i++) fin>>a[i];
    sort(a+1,a+n+1);
    for(int i=1;i<=n-2;i++)
        for(int j=i+1;j<=n-1;j++)
        {
            sol+=cautbin(a[i]+a[j],j,n,j);
        }
    fout<<sol<<"\n";
}