#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;
ifstream f("nrtri.in");
ofstream g("nrtri.out");
int a[805],n;
void read()
{
    f>>n; int i;
    for(i=1;i<=n;i++)
        f>>a[i];
    sort(a+1,a+n+1);
}
void solve()
{
    int i,j,u,p,mij,nr=0,ok;
    for(i=1;i<=n-2;i++)
    {
        for(j=i+1;j<=n-1;j++)
        {
            u=j+1; p=n; ok=-1;
            while(u<=p)
            {
                mij=(u+p)/2;
                if(a[mij]<=a[i]+a[j]){ u=mij+1; ok=mij; } else p=mij-1;
            }
            if(ok!=-1)nr+=ok-j;
        }
    }
    g<<nr;
}
int main()
{
    read();solve();
    return 0;
}