#include <fstream>
#include <algorithm>
using namespace std;
ifstream fin("nrtri.in");
ofstream fout("nrtri.out");
int v[805], n;
int caut(int st, int dr, int suma )
{
    int mij, sol = st - 1;
    while ( st <= dr )
    {
        mij = (st + dr) / 2;
        if ( v[mij] <= suma )
        {
            sol = mij;
            st = mij + 1;
        }
        else
            dr  = mij - 1;
    }
    return sol;
}
int main()
{
    int i, j;
    long long rasp = 0;
    fin >> n;
    for ( i = 1; i <= n; ++i )
        fin >> v[i];


    sort( v + 1, v + n + 1 );
    for ( i = 1; i <= n; ++i )
        for ( j = i + 1; j <= n; ++j )
            rasp = rasp + caut( j + 1, n, v[i] + v[j]) - j;


    fout << rasp << '\n';
    return 0;
}