Knights and Knaves

On an island, knights always tell the truth and knaves always lie. Five islanders A, B, C, D, E each make one statement. • [A:] "Exactly one of us is a knight." • [B:] "Exactly two of us are knights.'' • [C:] "Exactly three of us are knights.' • [ D:] "Exactly four of us are knights.'' • [E:] "All five of us are knaves.'' How many of the five are knights?