Consider the first 50 digits of Champernowne's constant

    0.12345678910111213141516171819202122232425262728293...

There are two zeros (do not count the left side of "." (integer part) ) in this series. So the digit concentration for 0 for the first 50 digits is = 2 / 50 = 0.04.

Also the number of '2' (x) digit is counted as 13. So the digit concentration of number '2' for the first 50 (d) digit is = 13/50 = 0.26

Calculate the digit concentration of number x for the first d digit of constant.