k = int(input())

A = [0 for _ in range(k + 7)]
B = [0 for _ in range(k + 7)]
for i in range(k + 1,k + 7):
    A[i] = 1
for i in range(k - 1, -1, -1):
    B[i] += 1
    for j in range(1, 7):
        A[i] += A[i + j] / 6
        B[i] += B[i + j] / 6
print(B[0] / (1 - A[0]))