B - Bob Learns To Read

Bob is just learning to read. He has difficulty reading some complex words, so you want to help him. Bob is given $2$ words $A$ and $B$, which he will read back to back (read $A$ completely then read $B$ completely). The difficulty for Bob arises whenever he reads a character that's not the same as the previous character he read. For example, if Bob is reading only the word $icpc$, he will find