K = int(input())
dp = [[0, 0] for _ in range(K+1)]
for i in range(K-1, -1, -1):
    x = 0
    for j in range(1, 7):
        if i+j > K:
            x += 1
            continue
        dp[i][0] += dp[i+j][0]/6
        dp[i][1] += dp[i+j][1]/6
    dp[i][0] += x/6
    dp[i][1] += 1
print(dp[0][1]/(1-dp[0][0]))