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)

n = int(input())
from collections import Counter
a = Counter(list(map(int,input().split()))).most_common()


cnt2 = []
cnt4 = []
for i in range(len(a)):
    if 2 <= a[i][1] <= 3:
        cnt2.append(a[i][0])
    if a[i][1] >= 4:
        cnt4.append(a[i][0])
    '''
    cnts[a[i]] += 1
    if cnts[a[i]] == 2:
        cnt2.append(a[i])
    if cnts[a[i]] == 4:
        cnt2.remove(a[i])
        cnt4.append(a[i])
        '''
ans = 0
if len(cnt2) <= 1 and not(cnt4):
    print(0)
else:
    if len(cnt2) >= 2:
        ans = max(ans, cnt2[-1]*cnt2[-2])
    if cnt4:
        ans = max(ans, cnt4[-1]**2)
    
    print(ans)