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: Wrong Answer)

N = int(input())
List = list(map(int,input().split()))
List_t = []
List_q = []
List.sort()
for x in range(N-1):
  if List[x]==List[x+1]:
    List_t.append(List[x])
for x in range(N-3):
  if List[x]==List[x+1]==List[x+2]==List[x+3]:
    List_q.append(List[x])

if len(List_q) == 0:
  if len(List_t)<=1:
    print(0)
  else:
    M = sorted(set(List_t))[-1]
    m = sorted(set(List_t))[-2]
    print(M*m)
else:
  M = sorted(set(List_q))[-1]
  print(M**2)