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 (3.4.3) (judge verdict: Accepted)

N = int(input())
ls = list(map(int,input().split()))
import collections
c = collections.Counter(ls)
unique_ls = list(reversed(sorted(([i[0] for i in c.items() if i[1] >= 2]))))

if len(unique_ls) >=2:
  if ls.count(unique_ls[0]) >=4:
    print(unique_ls[0]**2)
  else:
    print(unique_ls[0]*unique_ls[1])
elif len(unique_ls) ==1:
  if ls.count(unique_ls[0]) >=4:
    print(unique_ls[0]**2)
  else:
    print(0)
else:
  print(0)