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 (GCC 5.4.1) (judge verdict: Time Limit Exceeded)

#include <stdio.h>

int main(){
    int n, ans = 0;

    scanf("%d", &n);
 
    int l[n];
    for(int i = 0; i < n; i ++){
        scanf("%d", l + i);
    }

    for(int i = 0; i < n - 2; i ++){
        for (int j = i  + 1; j < n - 1; j ++){
            for(int k = j  + 1;k < n; k ++){
                if(l[i] < (l[j] + l[k]) && l[j] < (l[k] + l[i]) && l[k] < (l[i] + l[j])){
                ans ++;
                }
            }
        }
    }


    printf("%d", ans);
    return 0;
}