Chef and Alice

One day Chef and Alice tried a new way to make their messages encrypted. When they had to write something, firstly Chef wrote the message vertically in a matrix of *$N$* Columns. For example when they had to write "helloalicehowareyou" Chef wrote it like... h a h e e l o y l i w o l c a u o e r a If all the letters of the sentence were not sufficient to form a matrix they included