#include <fstream>
#include <algorithm>
using namespace std;
ifstream f("nrtri.in");
ofstream g("nrtri.out");
int v[801],n,sum,dr,st,mij,tri;
int main()
{

    f>>n;
    for (int i=1;i<=n;i++)
        f>>v[i];
    sort (v+1,v+n+1);
    for (int i=1;i<=n-2;i++)
    {
        for (int j=i+1;j<=n-1;j++)
        {
            sum=v[j]+v[i];
            st=j;
            dr=n+1;
            while (dr-st!=1)
            {
                mij=(st+dr)/2;
                if (v[mij]<=sum)
                    st=mij;
                else
                    dr=mij;
            }
            tri=tri+st-j;
        }
    }
    g<<tri;
    return 0;
}