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 = list(map(int,input().split()))
c = collections.Counter(A)
c_l = c.most_common()
if c_l[0][1] >= 2 and c_l[1][1] >= 2:
    ans1 = max(c_l[0][0],c_l[1][0])
    ans2 = min(c_l[0][0],c_l[1][0])
    for e in c_l:
        if e[0] > ans1:
            ans2 = ans1
            ans1 = e[0]
        elif e[0] > ans2:
            ans2 = e[0]
    print(ans1*ans2)
else:
    print(0)