#include <fstream>
#include <algorithm>
using namespace std;
int i,n,a[802],j,step,poz,st,dr,mij,nrt;
ifstream f ("nrtri.in");
ofstream g ("nrtri.out");
int main()
{
    f>>n;
    for (i=1;i<=n;i++)
    {
        f>>a[i];
    }
    sort (a+1,a+n+1);
    for (i=1;i<=n-2;i++)
    {
        for (j=i+1;j<=n-1;j++)
        {
            st=j+1;dr=n;poz=j;
            while (st<=dr)
            {
                mij=(st+dr)/2;
                if (a[mij]<=a[i]+a[j])
                {
                    poz=mij;
                    st=mij+1;
                }
                else dr=mij-1;
            }
            nrt+=poz-j;
        }
    }
    g<<nrt<<'\n';
    return 0;
}