Problem:
Score : 400 points

Problem Statement

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:

a < b + c

b < c + a

c < a + b

How many different triangles can be formed? Two triangles are considered different when there is a stick used in only one of them.

Constraints

All values in input are integers.

3 \leq N \leq 2 \times 10^3

1 \leq L_i \leq 10^3

Input

Input is given from Standard Input in the following format:

N
L_1 L_2 ... L_N

Constraints

Print the number of different triangles that can be formed.

Sample Input 1

4
3 4 2 1

Sample Output 1

1

Only one triangle can be formed: the triangle formed by the first, second, and third sticks.

Sample Input 2

3
1 1000 1

Sample Output 2

0

No triangles can be formed.

Sample Input 3

7
218 786 704 233 645 728 389

Sample Output 3

23

Solution in Perl (v5.18.2) (judge verdict: Time Limit Exceeded)

chomp($n = <>);
@s = sort {$a <=> $b} (split(/ /, <>));

$cnt = 0;
for $i (0 .. $#s - 2){
	for $p ($i + 1 .. $#s - 1){
		for $r ($p + 1 .. $#s){
			if($s[$r] >= ($s[$i] + $s[$p])){
				last;
			}else{
				$cnt++;
			}
		}
	}
}

print "$cnt\n";