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())
A = list(map(int, input().split()))

A.sort(reverse=1)

R = [0, 0]
r_ind = 0
a_ind = 0
while r_ind < 2 and a_ind < n-1:
    if A[a_ind] == A[a_ind + 1]:
        R[r_ind] = A[a_ind]
        a_ind += 2
        r_ind += 1
    else:
        a_ind += 1

print(R[0] * R[1])