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 (3.4.3) (judge verdict: Runtime Error)

# -*- coding: utf-8 -*-
"""
Created on Sun Sep 30 10:49:33 2018
ABC071C
@author: maezawa
"""
import collections
n = int(input())
a = list(map(int,input().split()))
acount = collections.Counter(a)
auniq = acount.keys()
auniq.sort(reverse=True)
edge1 = 0
ans = 0
for edge in auniq:
    if acount[edge] >= 4:
        if edge1 == 0:
            ans = edge*edge
            break
        else:
            ans = edge1*edge
            break
    if acount[edge] >= 2:
        if edge1 == 0:
            edge1 = edge
        else:
            ans = edge1*edge
            break
print(ans)