A company is giving the following commissions to its traders according to the city, in which they are working and the volume of sales s:
|City||0 <= s <= 500||500 < s <= 1000||1000 < s <= 10000||s > 10000|
Write a program that reads the name of a city (string) and the volume of sales (decimal number) and calculates the rate of the commission fee. The result has to be shown rounded up to 2 digits after the decimal point. When there is an invalid city or volume of sales (a negative number), print "error".