Problem:
Score : 300 points

Problem Statement

We have N sticks with negligible thickness.
The length of the i-th stick is A_i.

Snuke wants to select four different sticks from these sticks and form a rectangle (including a square), using the sticks as its sides.
Find the maximum possible area of the rectangle.

Constraints

4 \leq N \leq 10^5

1 \leq A_i \leq 10^9

A_i is an integer.

Input

Input is given from Standard Input in the following format:

N
A_1 A_2 ... A_N

Output

Print the maximum possible area of the rectangle.
If no rectangle can be formed, print 0.

Sample Input 1

6
3 1 2 4 2 1

Sample Output 1

2

1 \times 2 rectangle can be formed.

Sample Input 2

4
1 2 3 4

Sample Output 2

0

No rectangle can be formed.

Sample Input 3

10
3 3 3 3 4 4 4 5 5 5

Sample Output 3

20

Solution in Python (3.8.2) (judge verdict: Accepted)

# -*- coding: utf-8 -*-
"""
Created on Wed Sep 23 20:22:31 2020

@author: liang
"""

N = int(input())
A = [int(x) for x in input().split()]

A.sort(reverse=True)

ans = list()
i = 0
while i < N-1:
    if A[i] == A[i+1]:
       # print("A")
        ans.append(A[i])
        i += 1
    if len(ans) == 2:
        break
    i += 1

import numpy as np
#print(ans)
if len(ans) < 2:
    print(0)
else:
    print(np.prod(ans))