#include <fstream>
#include <algorithm>

using namespace std;

ifstream fin("nrtri.in");
ofstream fout("nrtri.out");

int n;
int a[802];


int main()
{
    fin >> n;
    for ( int i = 1; i <= n; ++i )
        fin >> a[i];
    sort( a + 1, a + n + 1 );
    int nr = 0;
    for ( int i = 1; i <= n - 2; ++i )
        for ( int j = i + 1; j <= n - 1; ++j )
    {
        int k = j + 1;
        while( a[i] + a[j] >= a[k] && k <= n )
               ++k;

         nr += k - j - 1;

    }

    fout << nr;

    fin.close();
    fout.close();
    return 0;
}