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 PyPy3 (2.4.0) (judge verdict: Wrong Answer)

# AtCoder
from collections import Counter
N = int(input())
A = list(map(int, input().split()))

c = Counter(A)
sc = sorted(c.items(), key=lambda x: x[0], reverse=True)
sides = set()
sei = 0
for side, nums in sc:
    if nums >= 4:
        sei = side

    if nums >= 2:
        sides.add(side)

sq = sei*sei
if 1 >= len(sides):
    if sq != 0:
        print(sq)
    else:
        print(0)
else:
    sl = sorted(list(sides), reverse=True)
    print(max(sl[0]*sl[1], sq))