Asterisk Pyramid

Given an integer (N) representing the number of levels, generate a pyramid of asterisks. The pyramid has (N) levels and each level (i) (starting from (i=0)) has (2i+1) asterisks. Each line should be centered such that the pyramid forms a symmetric shape. The maximum width of the pyramid is (2N-1). If (N \le 0), output an empty string.

For example, when (N = 4), the expected output is:

   *

*******</pre>

inputFormat

The input consists of a single integer (N) read from standard input, which indicates the number of levels for the pyramid.

outputFormat

Output the pyramid as a string to standard output. Each level should be on its own line. If (N \le 0), output nothing.## sample

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