K = int(input())


def check(m):
    dp = [1.0] * (K + 2)
    dp[-1] = m
    dp[K] = 0.0
    for i in range(K - 1, -1, -1):
        for j in range(1, 7):
            dp[i] += dp[min(i + j, K + 1)]/6
            
    return dp[0] <= dp[-1]

yes = 1e6
no = 0
for _ in range(60):
    mid = (yes + no)/2
    if check(mid):
        yes = mid
    else:
        no = mid
        
print(yes)