How much cat food is safe for dogs?

i've just gotten a new little puppy for christmas (russian toy terrier) i don't give him cat food but he does manage to steal some from my cats i've put their food up on a table so Riley (the pup) can't get it but skittles has always liked to take food from his dish an eat it else where so then the pup gets it i know the protein content is higher in cat food i wanted to know how much is too much for my lil Riley