Write a Python program that performs the following. Suppose that there are N events to be held this year. The ith event is scheduled from day si to day ti, and free food is to be served for that event every day from day si to ti (inclusive). Your task is to find out how many days there are in which free food is served by at least one event. Write a function called calculate that takes a list of strings containing the start and end days to solve this problem. Your main function will only read in the inputs and pass those inputs as a list to the calculate function (see the provided template for more information)