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
import sys

N = int(input())
A = list(map(int, input().split()))
c = collections.Counter(A)
two = [k for k, v in c.items() if v > 1]
four = [k for k, v in c.items() if v > 3]
if len(two) < 2 and not four:
    print(0)
    sys.exit(0)

St = 0
Sf = 0
if two:
    two.sort(reverse=True)
    St = 1
    for i in range(2):
        St *= two[i]
if four:
    Sf = max(four) * 2

print(St if St > Sf else Sf)