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)

N = int(input())
A = [int(a) for a in input().split(" ")]

A.sort(reverse=True)
l1 = 0
c1 = 0
l2 = 0
c2 = 0

L1 = 0
L2 = 0

for i in range(len(A)):
  if L1 and L2:
    break
  elif L1:
    if l2 == A[i]:
      c2 += 1
    elif l2 != A[i]:
      l2 = A[i]
      c2 = 1
    if c2 == 2:
      L2 = l2
  else:
    if l1 == A[i]:
      c1 += 1
    elif l1 != A[i]:
      l1 = A[i]
      c1 = 1
    if c1 == 2:
      L1 = l1

print(L1 * L2)