def solve(N):
    E = [0] * (N + 6)

    for x in list(range(N))[::-1]:
        E[x] = E[x+1] / 6 + E[x+2] / 6 + E[x+3] / 6 + E[x+4] / 6 + E[x+5] / 6 + E[x+6] / 6 + 1
    return E[0]


def main():
    N = int(input())
    print(solve(N))


if __name__ == '__main__':
    main()