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: Time Limit Exceeded)

N = int(input())
A = list(map(int,input().split()))
B = set(A)
C = sorted([i for i in B if A.count(i) // 2 >= 1],reverse = True)

ans = 0
m = 0
n = 0

if len(C) == 0:
 ans = 0
 
elif A.count(C[0]) >= 4:
  m = C[0]
  ans = m ** 2

elif len(C) > 1:
  m = C[0]
  n = C[1]
  ans = m * n

print(ans)