Prison

import random

def sim():
    l = list(range(100))
    random.shuffle(l)

    for i in range(100):
        step = 0
        prev = i
        while step < 50:
            next = l[prev]
            if next != i:
                prev = next
            else:
                break
            step += 1
        if next != i:
            return False
    return True

it = 100
print(sum(sim() for i in range(it))/it)