K = int(input())

dp = [-1]*(30)
for i in range(K,30):
    dp[i] = 0

def dfxx(x):
    if dp[x] >= 0:
        return dp[x]
    dp[x] = 0
    for i in range(1,7):
        dp[x] += dfxx(x+i)/6
    dp[x] += 1
    return dp[x]
print(dfxx(0))