Percy Jackson and the last Olympian

YA. Most people get presents on their sixteenth birthday. I get a prophecy that could save or destroy the world. This is the one where Kronos, Lord of the Titans, is beginning his attack on New York City, where Mount Olympus stands virtually unguarded. Oh, and the dreaded monster Typhon is also heading our way. So it's me and forty of my demigod friends versus untold evil.