#!/usr/bin/ python3.8
import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

K = int(read())

# 残りの数 -> 回数期待値は a + bx
A = [0] * (K + 10)
B = [0] * (K + 10)

for n in range(1, 7):
    A[-n] = 0
    B[-n] = 1

for n in range(1, K + 1):
    a = 0
    b = 0
    for i in range(1, 7):
        a += A[n - i]
        b += B[n - i]
    A[n] = 1 + a / 6
    B[n] = b / 6

a = A[K]
b = B[K]
answer = a / (1 - b)
print(answer)