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())
A=list(map(int,input().split()))

import collections
C=collections.Counter(A)
values,counts=zip(*C.most_common())
R=[]
for i in range(len(values)):
    R.append([values[i],counts[i]])
R.sort(reverse=True)

Long=0
Short=0

for i in range(len(values)):
    if R[i][1]>=4:
        Long=R[i][0]
        Short=R[i][0]
        break
    elif R[i][1]>=2 and Long==0:
        Long=R[i][0]
    elif R[i][1]>=2 and Long!=0:
        Short=R[i][0]
        break

print(Long*Short)