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

using namespace std;

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

int main() {
    int N;
    fin >> N;
    vector<int> a(N);
    for (int i = 0; i < N; ++i)
        fin >> a[i];

    sort(a.begin(), a.end());

    int count = 0;
    for (int i = 0; i < N - 2; ++i) {
        for (int j = i + 1; j < N - 1; ++j) {
            int sum = a[i] + a[j];
            auto it = upper_bound(a.begin() + j + 1, a.end(), sum - 1);
            count += it - (a.begin() + j + 1);
        }
    }

    fout << count << endl;
    return 0;
}