An international phone call is billed by the minute according to this scheme: Calls up to $10$ minutes cost a flat $$5.$ Calls over $10$ minutes but less than $30$ cost $$\mathrm{.}50$ per minute. Calls $30$ minutes or longer cost a base of $$15\mathrm{.}00$ plus $$\mathrm{.}30$ per minute over $30.$

Write a program to read in the duration of a call as an integer and output the total cost as a decimal. Do not worry about making it look like money.