#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;
ifstream fin("ntri.in");
ofstream fout("ntri.out");
int n,i,j,sol,f,s,d,m;
int a[801];
int main()
{
    fin>>n;
    for(i=1;i<=n;i++)fin>>a[i];
    sort(a+1,a+n+1);
    for(i=1;i<=n-2;i++)
        for(j=i+1;j<=n-1;j++)
    {
        s=j+1;
        d=n;
        m=n;
        while(s<=d)
        {
            m=(s+d)/2;
            if(a[i]+a[j]>a[m])s=m+1;
            else d=m-1;
        }
        sol+=d-j;
    }
    fout<<sol<<"\n";
    return 0;
}