K=int(input())

DP=[[0 for i in range(27)]for j in range(21)]
DP[0][0]=1
for i in range(20):
    for j in range(21):
        if j<K:
            for k in range(1,7):
                DP[i+1][j+k]+=DP[i][j]
#print(DP)
ans=0
for i in range(21):
    for j in range(27):
        if j>=K:
            ans+=((1/6)**i)*DP[i][j]*i
print(ans)