k = int(input())
dp = [0.0]*(k+1)
prob = [0.0]*(k+1)
prob[0] = 1.0
for i in range(1,k+1):
    r = 0.0
    for j in range(1,7):
        r += dp[i-j] if i-j > 0 else 0        
    dp[i] = 1.0 + r/6
    r = 0.0
    for j in range(1,7):
        r += prob[i-j] if i-j >= 0 else 0        
    prob[i] = r/6
print(dp[k]/prob[k])