某城市出租车收费标准如下： 起步里程为3公里，起步费10元； 超起步里程后10公里内（含10公里），每公里2元； 超过10公里以上的部分加收50%的回空补贴费，即每公里3元； 营运过程中，因路阻或乘客要求临时停车的，按每5分钟2元计收费（不足5分钟则不收费）。 编写程序，输入里程和停车时间，计算车费。

Null is a term used in computer programming and databases to represent a value that is absent or undefined. It is often used to indicate that a variable or field does not have a value assigned to it, or that a query or calculation did not produce a result. Null is also sometimes referred to as "nothing" or "empty." In some programming languages, null is represented by a special keyword or symbol, such as "null," "nil," or a zero-length string.