def solve():
    K = int(input())

    a = 0
    b = K * 100
    for i in range(100):
        c = (a + b) / 2

        dp = [0] * (K + 1)
        dp[0] = 0
        for i in range(1, K + 1):
            for j in range(1, 7):
                if i - j < 0:
                    dp[i] += c
                elif i - j > 0:
                    dp[i] += dp[i - j]
            dp[i] /= 6
            dp[i] += 1

        if dp[K] > c:
            a = c
        else:
            b = c

    print('{:.5f}'.format(b))


if __name__ == '__main__':
    solve()