Python3 代码

def calc_tax(income, base, limit, taxRate):
    tax = income - base
    if tax > limit and limit > -1:
        tax = limit
    return tax * taxRate

n = float(input())

tax = 0.0

if n > 2000:
    tax += calc_tax(n, 2000, 1000, 0.08)

if n > 3000:
    tax += calc_tax(n, 3000, 1500, 0.18)

if n > 4500:
    tax += calc_tax(n, 4500, -1, 0.28)

if tax > 0:
    print ("R$", f'{tax:.2f}')
else:
    print ("Isento")