Put Knight!

Petya and Gena play a very interesting game "Put a Knight!" on a chessboard n × n in size. In this game they take turns to put chess pieces called "knights" on the board so that no two knights could threat each other. A knight located in square (r, c) can threat squares (r - 1, c + 2), (r - 1, c - 2), (r + 1, c + 2), (r + 1, c - 2), (r - 2, c + 1), (r - 2, c - 1), (r + 2, c + 1) and (r + 2, c - 1) (some of the squares may be located outside the chessboard). The player who can't put a new knight during his move loses. Determine which player wins considering that both players play optimally well and Petya starts.