Ruby program to calculate generic root

Write a Ruby program to calculate generic root.

Generic Root: It sum of digits of a number unit we don't get a single digit.
Example:

Generic root of 4563: 4+5+6+3 = 18 since 18 is two digit numbers so 1 + 8 = 9
So, generic root of 4563 = 9

class GenericRoot

  def getGenericRoot

    sum = 0 

    rem = 0 

    print "Enter the number: "

    num = gets.chomp.to_i 

    while num >= 10 do

      sum = 0 

      while num != 0 do

        rem = num % 10 

        num = num / 10 

        sum += rem 

      end 

      (sum >= 10) ? (num = sum) : break

    end

    print "Generic root of given number is :" + sum.to_s

  end

end

p = GenericRoot.new 

p.getGenericRoot

Output:

Enter the number:  123456
Generic root of given number is :3