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)

a = input()
a_list = list(map(int, input().split()))
 
a_list = sorted(a_list, reverse=True)
 
big = 0
small = 0
min_a = min(a)

while True:
    max_a = max(a_list)
    counter = counter = a_list.count(max_a)
    if counter >= 4:
        if big == 0:
            big = max_a
        if small == 0:
            small = max_a
        break

    elif counter >= 2:
        if big == 0:
            big = max_a
        elif small == 0:
            small = max_a

    a_list.remove(max_a)
    if small != 0 or len(a_list) == 0:
        break

print(big*small)