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 C++14 (GCC 5.4.1) (judge verdict: Time Limit Exceeded)

#include <bits/stdc++.h>
#include <time.h>
using namespace std; 
int main()
{
	int a,b[3001],cnt=0;
	cin>>a;
	for (int i=0;i<a;i++)
		cin>>b[i];
	for (int i=0;i<a;i++)
		for (int n=i+1;n<a;n++)
			for (int m=n+1;m<a;m++)
				if (b[i]+b[n]>b[m]&&b[i]+b[m]>b[n]&&b[n]+b[m]>b[i])
					cnt++;
	cout<<cnt;
	return 0;
}