No, I don't think you should start it from the beginning again. I was just trying to help you think through the logic: whenever you are using negative logic it gets confusing quickly, particularly because English works the way you did it, so for example "it's not a donkey or a sheep" is actually expressed as "it's not a donkey AND it's not a sheep". Every animal, including donkeys and sheep, is "not a donkey OR not a sheep":
cat: not a donkey=TRUE; not a sheep=TRUE; TRUE+TRUE=TRUE (+=OR)
donkey: not a donkey=FALSE; not a sheep=TRUE; FALSE+TRUE=TRUE
sheep: not a donkey=TRUE; not a sheep=FALSE; TRUE+FALSE=TRUE
shonkey: not a donkey=FALSE; not a sheep=FALSE; FALSE+FALSE=FALSE
so the expression only evaluates FALSE for an animal that is both a donkey and a sheep, i.e. "not a donkey" and "not a sheep" are both FALSE.
So that is why your loop would never exit. Every character you entered was not S or not s, including both S and s.