import sys


def input(): return sys.stdin.readline().rstrip()


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

    ok = 0
    ng = K*6

    def solve(x):
        arr = [x] * 5 + [0]
        for i in range(K):
            arr = arr[1:] + [1 + sum(arr) / 6]

        return arr[-1] > x

    while abs(ok-ng) / max(1, ok, ng) > 1e-12:
        mi = (ok+ng)/2
        if solve(mi):
            ok = mi
        else:
            ng = mi

    print((ok+ng)/2)


if __name__ == '__main__':
    main()