In Self-Descriptor, we found a number ABCDEFGHIJ such that A is the count of how many 0's are in the number, B is the number of 1's, and so on.

I wonder... what if the number didn't have to be 10 digits long?

Find the smallest whole number such that the left-most digit describes the number of 0s in the number, the next digit describes the 1s, etc. Prove that it's the smallest.