import random

def newdeck(n):
    assert n % 2 == 0
    cards = (['red'] * (n/2)) + (['black'] * (n/2))
    random.shuffle(cards)
    return cards

def play():
    deck = newdeck(52)
    money = 0
    count = 0
    while deck:
        bet = False
        if count > 0:
            bet = True

        card = deck.pop()
        if bet:
            if card == 'red':
                money += 100
            else:
                money -= 100
        if card == 'red':
            count -= 1
        else:
            count += 1

        #print '%5s %5s %d' % (bet, card, money)

    return money

total = 0
trials = 1000
for i in range(trials):
    total += play()
print total / float(trials)