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: Wrong Answer)

#include <stdio.h>
int main()
{int n,A,B,C,count=0;
int i,j,k,temp;
scanf ("%d",&n);
int a[n];
for (i=0;i<n;i++)
{
    scanf ("%d",&a[i]);
}
//sorting

for (i=0;i<n-1;i++)
{
    for(j=i+1;j<n;j++)
    {
        if (a[i]>a[j])
        {
            temp=a[i];
            a[i]=a[j];
            a[j]=temp;
        }
    }
}

for (i=0;i<n;i++)
{ 
    A=a[i];
    for (j=i;j<n;j++)
    {
        B=a[j];
        for (k=j;k<n;k++)
        {   C=a[k];
            if (C<=A+B)
            {
                break;
            }
            count++;
        }
    }

}
printf ("%d",count);
}