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.

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.

Constraints

• $4 \leq N \leq 10^5$
• $1 \leq A_i \leq 10^9$
• A_i is an integer.

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

见题面 Input 部分

见题面 Output 部分