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)

from collections import Counter


def main():
    N = int(input())
    A = list(map(int, input().split(' ')))
    counter = Counter(A)
    dupl_bars = [length for length, cnt in counter.items() if cnt > 1]
    dupl_bars.sort(reverse=True)
    if len(dupl_bars) > 1:
        if counter[dupl_bars[0]] > 3:
            print(dupl_bars[0] ** 2)
        else:
            print(dupl_bars[0] * dupl_bars[1])
    else:
        print(0)


if __name__ == '__main__':
    main()