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 (7.3.0) (judge verdict: Accepted)

from collections import Counter
n = int(input())
a = list(map(int, input().split()))
count_a = Counter(a)
new_a = [i for i in count_a.keys() if count_a[i] >= 2]
#print(new_a)
if len(new_a) < 2:
    print(0)
    exit()
new_a = sorted(new_a, reverse=True)
if count_a[new_a[0]] >= 4:
    ans = new_a[0] ** 2
else:
    ans = new_a[0] * new_a[1]
print(ans)