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-----
6
3 1 2 4 2 1

-----Sample Output-----
2

$1 \times 2$ rectangle can be formed.

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