#include <fstream>
#include <algorithm>

using namespace std;

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

int A[805], n, numi;

int main()
{
    f >> n;
    for(int i = 1; i <= n; i ++)
        f >> A[i];

    for(int i = 1; i < n - 1; i ++)
        for(int j = i + 1; j < n; j ++)
        {
            int st = j, dr = n, poz = j;
            while(st <= dr)
            {
                int m = (st + dr) / 2;
                if(A[m] <= A[i] + A[j])
                    st = m + 1, poz = m;
                else
                    dr = m - 1;
            }

            numi += (poz - j);
        }

    g << numi;
    return 0;
}