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.*;

public class Main{
    public static void main(String args[]){
        Scanner scanner = new Scanner(System.in);
        int N = scanner.nextInt();
        List<Integer> L = new ArrayList<>(); 
        for(int i=0; i<N; i++){
            L.add(scanner.nextInt());
        }

        Collections.sort(L);
        int count = 0;
        for(int i=0; i<N; i++){
            for(int j=i+1; j<N; j++){
                for(int k=j+1; k<N; k++){
                    int a = L.get(i);
                    int b = L.get(j);
                    int c = L.get(k);
                    if(a+b>c && a+c>b && b+c>a){
                        count++;
                    }else{
                        break;
                    }
                }
            }
        }
        System.out.println(count);
    }
}