def main():
    # DP[i]・・・今までの和がiで、あと何回振らなきゃいけないか
    #にぶたんばーじょん
    k = int(input())
    dp = [0] * (k + 1)
    roop = 20
    l = 0
    r = k + 6
    for _ in range(roop):
        m=(l+r)/2
        dp[0]=m
        for i in range(k - 1, -1, -1):
            dp[i] = sum(dp[i + j] if i + j <= k else dp[0] for j in range(1, 7)) / 6 + 1
        if dp[0]>m:l=m
        else:r=m
    print(l)

main()