Numbers Factory

You are given a two or more digits number **N**.
For this mission, you should find the smallest positive number of **X**,
such that the product of its digits is equal to N.
If X does not exist, then return 0.

Let's examine the example. N = 20. We can factorize this number as 2*10, but 10 is not a digit. Also we can factorize it as 4*5 or 2*2*5. The smallest number for 2*2*5 is 225, for 4*5 -- 45. So we select 45.

... Remember prime numbers (numbers divisible by only one) and be careful with endless loops.

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