Purpose:

Practice use of UMPIRE method to solve problems.

Problem Statement:

Find the last digit of the factorial of a given non$-$negative number, $n.$

Example $1$:

Input: $n=4$

Output: $4$

Explanation: $n24,$ the last digit of which is $4.$

Example $2$:

Input: $n=5$

Output: $0$

Explanation: $n120,$ the last digit of which is $0.$

Constraints:

$0n5**106$

Criteria: