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 (3.8.2) (judge verdict: Accepted)

import collections

def main():
    N = int(input())
    A = list(map(int, input().split()))
    rankA = list(set(A))
    rankA.sort(reverse=True)
    Acounter = collections.Counter(A)
    res = 4
    ans = []
    for a in rankA:
        count = Acounter[a]
        if count >= 2:
            ans.append(a)
            res = res - 2
            count = count - 2
            if len(ans) == 2:
                break
            if count >= 2:
                ans.append(a)
                break

    if len(ans) < 2:
        print(0)
        return

    a1 = ans.pop()
    a2 = ans.pop()
    ans = a1*a2
    print(ans)

if __name__ == "__main__":
    main()