#include <fstream>
using namespace std;

ifstream is("nrtri.in");
ofstream os("nrtri.out");

int Cautbin( int st );

int n, a[1000], l;
int mij, st, dr;
int s;
int aux;
int nrtri;

int main()
{
    is >> n;
    for(int i = 1; i  <= n; ++i)
    {
        is >> a[i];
    }
    for(int i = 1; i <= n; ++i )
    {
        for(int j = i + 1; j <= n; ++j)
        {
            if(a[i] > a[j])
            {
                aux = a[i];
                a[i] =a[j];
                a[j] = aux;
            }
        }
    }
    for(int i = 1; i <= n - 2; ++i)
    {
        for(int j = i + 1; j <= n - 1; ++j)
        {
            s = a[i]+ a[j];
            nrtri += Cautbin(j) - j - 1;
        }
    }
    os << nrtri;
    is.close();
    os.close();
    return 0;
}
int Cautbin( int st )
{
    dr = n;
    while ( st < dr )
    {
        mij = (st + dr) / 2;
        if( a[mij] > s )
            dr = mij - 1;
        else
            st = mij + 1;
    }
    if( s >= a[dr] )
        ++dr;
    return dr;
}