Changes

If there is one file name provided at the command line, read the login /logout records from the contents of the given file. The format of each line in the file should be the same as the output of 'last -Fiw'. Filter out incomplete login/logout record (check for the number of fields in each record).

If there is more than one file name provided, merges merge all the files together with the first one at the top and the last one at the bottom. Read and process the file contents in that order in your program.