#include <fstream>
#include <algorithm>
#define NMAX 800
#define LIMIT 15

using namespace std;

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

int n, S;
int v[NMAX];

void cautareBinara(int i, int j) {
    int pas = 1 << LIMIT, r = 0, lung = v[i] + v[j];
    while (pas != 0) {
        if (r + pas < n && v[r + pas] <= lung) {
            r += pas;
        }
        pas >>= 1;
    }
    //out << i << ' ' << j << ' ' << r << '\n';
    S += r - j;
}

int main()
{
    in >> n;
    for (int i = 0; i < n; i++) {
        in >> v[i];
    }
    sort(v, v + n);
    for (int i = 0; i < n; i++) {
        for (int j = i + 1; j < n; j++) {
            cautareBinara(i, j);
        }
    }
    out << S;
    return 0;
}