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

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


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


if __name__ == '__main__':
    main()