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
k=list(collections.Counter(a).items())
x=[k[i][0] for i in range(len(k)) if 2<=k[i][1]<4]
y=[k[i][0] for i in range(len(k)) if k[i][1]>=4]
x.sort()
y.sort()
if len(x)>1 and len(y)>1:
    print(max(x[-1]*x[-2], y[-1]**2))
elif len(x)>1:
    print(x[-1]*x[-2])
else:
    print(0)