k = int(input())
dp = [0] * 500

for i in range(10000):
    for i in range(1, k+1):
        tmp = 6
        for j in range(1, 7):
            if i - j < 0:
                tmp += dp[k]
            else:
                tmp += dp[i - j]
                
        dp[i] = tmp / 6
        
print(dp[k])