Playing Cards

Bob is having a deck of $N$ playing cards. In this deck each of the cards is asssociated with a power level. Bob is shuffeling the deck. In each of the shuffle he takes out any continous segment of cards from the deck and keeps it at the top of the deck. Every time he shuffles, he chooses a random number and wonders what is the maximum length of continous subsegment he can take out from the deck s