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: Accepted)

import collections as c
import sys
N = int(input())
A = c.Counter(list(map(int, input().split())))

key = list(A.keys())
val = list(A.values())

quad = [key[i] for i in range(len(key)) if val[i] >= 4]
if len(quad) >= 1:
	quad = max(quad)
else:
	quad = 0

bi = sorted([key[i] for i in range(len(key)) if val[i] >= 2], reverse = True)
if len(bi) >= 2:
	bi_1 = bi[0]
	bi_2 = bi[1]
else:
	bi_1 = 0
	bi_2 = 0

print(max(quad**2, bi_1*bi_2))