Perfect.java: Write a program that reads in an integer N from the keyboard, and displays whether N is a "perfect number" or not (Yes or No). A number is "perfect" if it is equal to the sum of all of its factors (not including itself as a factor, but including 1 as a factor). 6 is the first perfect number, because its factors are 1, 2, and 3, and 1+2+3 = 6.