def E(x):
    if x in memo:
        return memo[x]
    if x >= K:
        return 0
    P = 1 / 6
    ret = 1
    for i in range(1,7):
        ret += E(x+i) * P
    memo[x] = ret
    return ret

K = int(input())
memo = {}
print(E(0))