# include <fstream>
# include <algorithm>

using namespace std;

ifstream f ( "nrtri.in" );
ofstream g ( "nrtri.out" );

int a[805], n, nrtri, k;

int main ()
{
    register int i;
    register int j;

    f >> n;
    for ( i = 1; i <= n; i ++ )
        f >> a[i];

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

    for ( i = 1; i < n - 1; i ++ )
    {
        for ( j = i + 1; j < n; j ++ )
        {
            k = j + 1;
            while ( k <= n && a[i] + a[j] <= a[k] )
            {
                k ++;
                nrtri ++;
            }
        }

    }

    g << nrtri;

    return 0;
}