def years_to_double(money, rate):

    '''Return how many (complete) years it takes for an investment to
       double at a given interest rate.'''

    years = 0

    # Each year until the investment has doubled, add 
    # interest for the year.
    while money != (money * 2): 
        years += 1
        money += rate * money
    return years

def main():
    
    # How many years will it take to turn 10 dollars into 20 dollars
    # if 10% interest is added every year?
    interest = 0.1
    investment = 10
    years = years_to_double(investment, interest)
    print(years,"sb 8")

    #here is a nicer print statement
    print("At an interest rate of " + str(interest*100) + "%") 
    print("your money will double in " + str(years) + " years.")



main()