Tradermath logoBrainteaser - Christmas Cards

Christmas Cards
You have \( N \) uniquely addressed Christmas cards, each meant for one of your \( N \) friends. However, in a mix-up, you've jumbled up the addresses. Without knowing which card goes to which friend, you randomly assign each card to an address (ensuring each friend gets one card). What is the expected number of cards that end up being sent to the correct friend?