Second Smallest Unique Number

You are given a list of integers. Your task is to find the second smallest unique number in the list. If the list does not contain at least two unique numbers, output None.

In mathematical terms, if the unique elements of the list are sorted in ascending order as $$a_1, a_2, \ldots, a_k$$ where $$k \ge 1$$, then you need to output $$a_2$$ if $$k \ge 2$$; otherwise, output None.

Note: The input will be provided via standard input (stdin) and the output should be printed to standard output (stdout).

inputFormat

The first line of input contains an integer n — the number of elements in the list. The second line contains n space-separated integers representing the list.

Example:

5
3 1 5 2 4

outputFormat

Output a single line containing the second smallest unique integer in the list. If there is no such number, output None.

Example:

2

## sample

5
3 1 5 2 4

2