Objective
Today, we're learning and practicing an algorithmic concept called Recursion. Check out the Tutorial tab for learning materials and an instructional video!
Recursive Method for Calculating Factorial
Task
Write a factorial function that takes a positive integer,  as a parameter and prints the result of  ( factorial).
Note: If you fail to use recursion or fail to name your recursive function factorial or Factorial, you will get a score of .
Input Format
A single integer,  (the argument to pass to factorial).
Constraints
  • Your submission must contain a recursive function named factorial.
Output Format
Print a single integer denoting .
Sample Input
3
Sample Output
6
Explanation
Consider the following steps:
From steps  and , we can say ; then when we apply the value from  to step , we get . Thus, we print  as our answer.

Here is the Solution
N = gets.to_i
def factorial(num)
if num == 0 || num == 1
return 1
end
return num * factorial(num-1)
end
print factorial N