K = int(input())
E = [0 for i in range(27)]

for i in range(K,27):
    E[i] = 0
E[K-1] = 1.0

for i in range(K-2,-1,-1):
    for j in range(1,7):
        E[i] += E[i+j] / 6.0
    E[i] += 1.0

print(E[0])