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 = sorted(list(map(int,input().split())),reverse=True)
a += [0]
b = -1
ans = [0,0]
count = 0
for i in range(n+1):
    count += 1
    if b != a[i]:
        if count >= 4:
            if ans[0]:
                ans[1] = b
                break
            else:
                ans[0] = b
                ans[1] = b
                break
        elif count >= 2:
            if ans[0]:
                ans[1] = b
                break
            else:ans[0] = b
        b = a[i]
        count = 0
print(ans[0]*ans[1])