#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>

using namespace std;

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

const int Nmax = 850;

int N, LG, sol, V[Nmax];

int main()
{
    fin >> N;
    for(int i = 1; i <= N; i++)
        fin >> V[i];
    sort(V + 1, V + N + 1);

    for(LG = 1; LG <= N; LG <<= 1);

    int lg, k;
    for(int i = 1; i < N - 1; i++)
        for(int j = i + 1; j < N; j++)
        {
           for(k = j, lg = LG; lg; lg >>= 1)
                if(k + lg <= N && V[k + lg] <= V[i] + V[j])
                    k += lg;
            sol += k - j;
        }
    fout << sol;
    return 0;
}