#include <fstream>
#include <algorithm>

using namespace std;

ifstream F ("nrtri.in");
ofstream G ("nrtri.out");

int i,j,st,dr,k,n,v[802],mijl;
int main()
{
    F>>n;
    for ( i=1;i<=n;i++ )
        F>>v[i];

    sort (v+1,v+n+1);

    for (i=1;i<=n-2;i++)
    {
        for (j=i+1;j<=n-1;j++)
        {
            st=j+1;dr=n;
            while (st<=dr)
            {
                mijl=(st+dr)/2;
                if ( v[i]+v[j]>=v[mijl] )
                    st=mijl+1;
                else
                    dr=mijl-1;
            }
            k+=dr-j;
        }
    }

    G<<k;
    return 0;
}