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 Java8 (OpenJDK 1.8.0) (judge verdict: Time Limit Exceeded)

import java.util.Arrays;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int s[] = new int[n];
		int ans = 0;
		for (int i = 0; i < n; i++) {
			s[i] = sc.nextInt();
		}
		Arrays.sort(s);
		for (int i = 0; i < n - 2; i++) {
			for (int o = i + 1; o < n - 1; o++) {
				// s[i]+s[o]
				for (int p = o + 1; p < n; p++) {
					if ((s[i] + s[o] > s[p])
							&& (Math.abs(s[i] - s[o]) < s[p])) {
						//System.out.println(s[i]+" "+s[o]+" "+s[p]);
						ans++;
					}
				}

			}

		}
	System.out.println(ans);
	}
}