K = int(input())
DP = [0]*(K+2)
KAKURITU = [[0]*201 for i in range(201)]
KAKURITU[0][0]=1

for i in range(201):
    for j in range(201):
        if KAKURITU[i][j]:
            for k in range(1,7):
                if j+k<=200:
                    KAKURITU[i+1][j+k]+=KAKURITU[i][j]/6

kakuritu = 0
for i in range(201):
    kakuritu+=KAKURITU[i][K]




def dfs(wa,kitai):
    if wa>=K:
        return 0
    if DP[wa]:
        return DP[wa]
    temp = 0
    for i in range(1,7):
        temp += (dfs(wa+i,kitai+1)+1)/6
    DP[wa] = temp
    return DP[wa]

dfs(0,0)
print(DP[0]/kakuritu)