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: Accepted)

N = int(input())
numList = list(map(int, input().split()))
numList.sort(reverse = True)

target1 = False
target2 = False

i = 0

while i < N-1:
    if numList[i] == numList[i+1]:
        if target1 == False:
            num1 = numList[i]
            target1 = True
            i += 1
        elif target1 == True:
            num2 = numList[i]
            target2 = True
    if target1 == True and target2 == True:
        break
    i += 1

if target2 == False:
    print("0")
else:
    print(num1 * num2)