#include <fstream>

int v[801];

int main() {
    std::ifstream in("nrtri.in");
    std::ofstream out("nrtri.out");
    int i, j, n, r, pas, s = 0;
    in >> n;
    for (i = 1; i <= n; i++) in >> v[i];
    for (i = 1; i <= n - 2; i++) {
        for (j = i + 1; j <= n - 1; j++) {
            r = j;
            pas = 1 << 9;
            while (pas != 0) {
                if (r + pas <= n && v[r + pas] <= v[i] + v[j]) r += pas;
                pas >>= 1;
            }
            s += r - j;
        }
    }
    out << s;
    return 0;
}