# average annual tuition increase (3.86%)
ANNUAL_INCREASE = 0.0386

# tuition cost 2015-16
COST_2015 = 61354    
    

def years_to_cost_iter(cur_cost, target_cost):
    '''Return the numbers of years until Bowdoin tuition
    will reach target_cost, assuming the current cost is cur_cost.
    ITERATIVE implementation.'''
    years_passed = 0
    cost = cur_cost
    while cost < target_cost:
        cost *= 1 + ANNUAL_INCREASE
        years_passed += 1
    return years_passed


def years_to_cost(cur_cost, target_cost):
    '''Return the numbers of years until Bowdoin tuition
    will reach target_cost, assuming the current cost is cur_cost.
    RECURSIVE implementation.'''
    if cur_cost >= target_cost: # base case
        return 0
    else: # recursive case
        next_cost = cur_cost + ANNUAL_INCREASE * cur_cost
        return 1 + years_to_cost(next_cost, target_cost)


def main():
    '''Prompt for a future cost, then calculate how many years it will take
    for tuition to reach that cost.'''
    print("Current cost is ${0}".format(COST_2015))
    future_cost = int(input("Enter a future cost: "))
    years = years_to_cost(COST_2015, future_cost)
    print("Tuition will reach ${0} in {1} years".format(future_cost, years))
    
main()