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)

import collections

n = int(input())
a = [int(_) for _ in input().split()]
aa = collections.Counter(a).most_common()
aa = sorted(aa, reverse=True)
length = []
cnt = 0
for i in aa:
    if i[1] >= 2:
        length.append(i)
        cnt += 1
        if cnt == 2:
            break
    else:
        pass
if cnt >= 2:
    print(length[0][0] * length[1][0])
elif cnt == 1 and length[0][1] >= 4:
    print(length[0][0] * length[0][0])
else:
    print(0)