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)

import collections
n = int(input())
a = list(map(str,input().split()))
c = collections.Counter(a)
set_a = set(a)
lists = []
for i in set_a:
    if int(c[i]) == 2:
        lists.append(i)
    elif int(c[i]) == 3:
        lists.append(i)
    elif int(c[i]) >= 4:
        lists.append(i)
        lists.append(i)

lists.sort()
lists.reverse()
Max = -999999999
if len(lists) > 1:
    for i in range(len(lists)-1):
        ans = int(lists[i]) * int(lists[i+1])
        if ans > Max:
            Max = ans
else:
    Max = 0
print(Max)