import collections

def solve(K):
    frontiers = {0: 1.0}
    pK = [0] * 6
    dp = [0] * 6
    if K <= 5:
        pK[K] = 1.0
    for i in range(1, K + 1):
        new_frontiers = collections.defaultdict(float)
        for v, p in frontiers.items():
            p6 = p / 6
            for dv in range(1, 7):
                nv = v + dv
                if nv > K:
                    continue
                if 5 >= K - nv:
                    pK[K - nv] += p6
                    dp[K - nv] += i * p6
                new_frontiers[nv] += p6
        frontiers = new_frontiers
    a = sum((dp[i] + pK[i]) * (6 - i) for i in range(6))
    b = 6 - sum(pK[i] * (6 - i) for i in range(1, 6))
    return a / b - 1

K = int(input())
print(solve(K))