def ryad(n):
    """
    Считаем количество занятых мест в ряду
    """
    import random
    count=0
    all_seats = set(zip(range(n-1),range(1,n)))
    while len(all_seats)!=0:
        a = random.sample(all_seats,1)
        seat_copy = all_seats.copy()
        for i in seat_copy:
            #if (a[0][0]-i[0]==1 and a[0][1]-i[1]==1) or (i[0]-a[0][0]==1 and i[1]-a[0][1]==1):
            if (a[0][0]-i[0]==1 and a[0][1]-i[1]==1) or (i[0]-a[0][0]==1 and i[1]-a[0][1]==1):
                all_seats.discard(i)
                #print(a[0][0],a[0][1],i[0],i[1])
        all_seats.discard(a[0])
        count+=1
    return count

n=1000
M=100
count_all=0
for _ in range(M):
    count_all+=ryad(n)
print(1-((2*count_all)/(M*n)))