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

using namespace std;

void inssort(int v[], int n) {
    int i, j, x;
    for (i = 0; i < n; i++) {
        x = v[i];
        for (j = i - 1; x < v[j] && j >= 0; j--) {
            v[j + 1] = v[j];
        }
        v[j + 1] = x;
    }
}

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

    while (st <= dr) {
        mid = (st + dr) / 2;

        if (v[mid] > val) {
            dr = mid - 1;
        }
        else if (v[mid] < val) {
            st = mid + 1;
        }
        else {
            break;
        }
    }

    return dr;
}

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];
    }

    inssort(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 (v[x] <= i + j)
                nr += x - j;
        }
    }

    fout << nr;

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