Using Matlab. Everytime I try to use the function it tells me function error

Write a function nexthour that receives one integer argument, which is an hour of the day, and returns the next hour. This assumes a 12-hour clock; so, for example, the next hour after 12 would be 1. If it receives one integer greater than 12 or less then 0, the function will instead return a flag of -100.

Here are examples of using this function: >>nexthour(12)

ans= 1

>>nexthour(2)

ans= 3

>>nexthour(-20)

ans= 100