memo = {}
def f(x: int, p: float) -> float:
    if x < 0: return p
    if x == 0: return 0
    if x in memo: return memo[x]

    res = 0
    for i in range(1, 7):
        res += (f(x-i, p) + 1) / 6

    memo[x] = res
    return res


K = int(input())

lo = 1
hi = 1 << 60
ans = hi
for i in range(100):
    p = (lo + hi) / 2
    memo.clear()
    if f(K, p) <= p:
        ans = min(ans, p)
        hi = p
    else:
        lo = p

print(f'{ans:.10f}')