Unique Paths in a Square Grid

You are given a positive integer n representing the dimensions of a square grid. Your task is to compute the number of unique paths from the top-left corner to the bottom-right corner when you are only allowed to move either to the right or down.

The number of unique paths in an n × n grid is given by the formula:

If the input is not a positive integer, the result should be 0.

Note: The input is read from stdin and the output must be printed to stdout.

inputFormat

A single line containing a value which should represent a positive integer n. If the value cannot be parsed as a positive integer, then output should be 0.

outputFormat

A single line containing the number of unique paths from the top-left corner to the bottom-right corner of an n × n grid (using only right and down moves). Output 0 for invalid input.## sample

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