K = int(input())

E = [0 for i in range(K+7)]
E[K+6] = 0
E[K+5] = 0
E[K+4] = 0
E[K+3] = 0
E[K+2] = 0
E[K+1] = 0
E[K] = 0

for i in reversed(range(K)):
    E[i] = E[i+1]/6 + E[i+2]/6 + E[i+3]/6 + \
           E[i+4]/6 + E[i+5]/6 + E[i+6]/6 + 1

print(format(E[0], '.4f'))