-----Description-----  
This task requires writing a Lean 4 method that extracts the last digit of a given non-negative integer. The method should return the last digit, which is obtained by computing the remainder when the number is divided by 10. The result must always be between 0 and 9.

-----Input-----  
The input consists of a single value:  
n: A non-negative integer.

-----Output-----  
The output is an integer:  
Returns the last digit of the input number, ensuring that the digit lies within the range 0 to 9.

-----Note-----  
It is assumed that the input number n is non-negative.