#include <fstream>
#include <stdio.h>
#include <algorithm>

using namespace std;

//return ultimul <= val
int cautbin(int v[], int st, int dr, int val) {
    int mid = (st + dr) / 2;

    if (v[st] > val) {
        return -1;
    }

    if (st == dr) {
        return st;
    }

    if (v[mid] > val) {
        return cautbin(v, st, mid, val);
    } else {
        return cautbin(v, mid, dr - 1, val);
    }
}

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

    int N, v[800], nr = 0;

    fin >> N;

    for (int i = 0; i < N; i++) {
        fin >> v[i];
    }

    sort(v, v + N);

    for (int i = 0; i < N - 2; i++) {
        for (int j = i + 1; j < N - 1; j++) {
            int x = cautbin(v, j + 1, N - 1, v[i] + v[j]);

            if (x != -1) {
                nr += x - j;
            }
        }
    }

    fout << nr;

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