100712: [AtCoder]ABC071 C - Make a Rectangle

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