Zero quintuples#7448
You are given a sequence of distinct integers a_1, a_2, \dots, a_n.
A zero quintuple is a set of five elements a_i, a_j, a_k, a_p, a_q such that i < j < k < p < q and
Find the number of different zero quintuples in the given sequence.
The first line contains an integer n~(5 \le n \le 2000) — the number of elements in the sequence.
The second line contains distinct integers a_1, a_2, \dots, a_n~(-10000 \le a_i \le 10000) — the elements of the sequence.
Print one integer — the number of zero quintuples in the given sequence.
Örnek 1