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 PyPy3 (2.4.0) (judge verdict: Time Limit Exceeded)

n=int(input())
L_lst=sorted(list(map(int,input().split())))
i=n-2
j=n-1
cnt=0
while j>1:
    for x in range(i-1,-1,-1):
        if x==0:#0だとout of range
            if L_lst[x]+L_lst[i]>L_lst[j]:
                cnt+=1
        else:
            if L_lst[x]!=L_lst[x-1]:
                if L_lst[x]+L_lst[i]>L_lst[j]:
                    cnt+=1
                else:
                    break
    i-=1
    if i==0 or (L_lst[j])//2 >= L_lst[i]:
        j-=1
        i=j-1
print(cnt)