k=int(input())
F=[0.0]*(k+1)
G=[0.0]*(k+1)
a=1/6

for i in range(k-1,-1,-1):
    for j in range(1,7):
        if(i+j<=k):
            F[i]+=F[i+j]*a
            G[i]+=G[i+j]*a
        else:
            F[i]+=a
    G[i]+=1

print(G[0]/(1-F[0]))