#include <fstream>
#include <algorithm>
using namespace std;

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

int n, a[801], nrtri;

int main()
{
    is >> n;
    for ( int i = 0; i < n; i++ )
        is >> a[i];
    sort( a, a + n );
    for ( int i = 0; i < n - 2; i++ )
        for ( int j = i + 1; a[i] + a[j] >= a[j+1] && j < n - 1; j++ )
            nrtri++;
    os << nrtri;
    is.close();
    os.close();
    return 0;
}