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)

N = int(input())
lst_A = list(map(int, input().split()))
lst_A.sort(reverse=True)
cur_a = -1
lst_ans = []


for i, a in enumerate(lst_A):
    if cur_a == a:
        lst_ans.append(a)
        cur_a = -1
        if len(lst_ans) == 2:
            break
    else:
        cur_a = a


ans = lst_ans[0] * lst_ans[1] if len(lst_ans) else 0
print(ans)