Score : 400 points
Takahashi has N sticks that are distinguishable from each other. The length of the i-th stick is L_i.
He is going to form a triangle using three of these sticks. Let a, b, and c be the lengths of the three sticks used. Here, all of the following conditions must be satisfied:
How many different triangles can be formed? Two triangles are considered different when there is a stick used in only one of them.
Input is given from Standard Input in the following format:
N L_1 L_2 ... L_N
Print the number of different triangles that can be formed.
4 3 4 2 1
1
Only one triangle can be formed: the triangle formed by the first, second, and third sticks.
3 1 1000 1
0
No triangles can be formed.
7 218 786 704 233 645 728 389
23