编程题：Prime Number

Your program reads a natural number in and judge if it is a prime number or not.

### Input Format:

A positive whole number.

### Output Format:

A sentence states the number is prime or composite.

### Sample Input:
in
13


### Sample Output:

out
13 is a prime number.


### Sample Input:
in
12


### Sample Output:

out
12 is not a prime number.












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