balance = 320000
annualInterestRate = 0.2

low = balance / 12.0
high = balance
guess = (high + low) / 2.0

while True:
    tempBal = balance
    for month in range(1, 13):
        tempBal -= guess  # remove guess from the unpaid balance
        tempBal += (annualInterestRate/12.0) * tempBal  # calculate the monthly interest and add the monthly interest to the balance

    if tempBal <= 0:
        break
    else:
        if guess < tempBal:
            low = guess
        else:
            high = guess
        guess = (high + low) / 2.0

print('Lowest Payment: ', round(guess))