def collatz(number):
    global collatzstart
    if number % 2 == 0:
        collatzstart = number // 2
        print(collatzstart)
        return collatzstart
    else:
        collatzstart = 3 * number + 1
        print(collatzstart)
        return collatzstart

print('Hello, we\'re going to explore the Collatz sequence!')
print('Please select a whole positive number.')

while True:
    collatzstart = (input())
    try:
        collatzstart = int(collatzstart)
        break
    except ValueError:
        print('That\'s not a whole positive number :(')
        print('Please try again.')

while collatz(collatzstart) != 1:
    collatz(collatzstart)