from collections import *
from itertools import *
from functools import *
from heapq import *
import sys,math,time,random
input = sys.stdin.readline
start = time.time()
K = int(input())

cnt = 0
S = 0

while time.time() - start < 4:

    T = 0
    tS = 0
    while True:

        T += random.randint(1,6)
        tS += 1
        if T>K:
            T = 0
        if T==K:
            break
    S += tS
    cnt += 1
print(S/cnt)