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: Wrong Answer)

#N = int(input())
A = list(map(int, input().split()))

asum = {}
for a in A:
	if a not in asum:
		asum[a] = 1
	else:
		asum[a] += 1

#print(asum)

kouho = 0
for a in sorted(asum)[::-1]:
	if 4 <= asum[a]:
		if kouho:
			print(kouho * a)
		else:
			print(a * a)
		break
	elif 2 <= asum[a]:
		if kouho:
			print(kouho * a)
			break
		else:
			kouho = a
else:
	print(0)