k = int(input())


def calc(x):
    dp = [0]*(k+1)
    dp[k] = 0
    for i in range(k)[::-1]:
        count = 0
        for j in range(1,7):
            if i+j <= k:
                count += dp[i+j]
            else:
                count += x
        dp[i] = count/6+1

    return dp[0]

l = 0
r = 10**10

for i in range(80):
    m = (r+l)/2
    if calc(m) > m:
        l = m
    else:
        r = m
print(l)