Can you find the digit?

$S=123456789101112131415161718192021\ldots$

Given that the string $S$ is the concatenation of the first 1,000,000,000 positive integers in ascending order, find the $999999999^{\text{th}}$ digit of $S$.

Details and Assumptions:

By the $x^{\text{th}}$ digit of $S$, we mean the digit in the $x^{\text{th}}$ place from the left in the decimal representation of $S$.

Some explicit examples are :

• The $5^{\text{th}}$ digit of the number $14583469$ is $3$.
• The $4^{\text{th}}$ digit of the number $143256$ is $2$.