import sys
def I(): return int(sys.stdin.readline().rstrip())
def MI(): return map(int,sys.stdin.readline().rstrip().split())
def LI(): return list(map(int,sys.stdin.readline().rstrip().split()))
def LI2(): return list(map(int,sys.stdin.readline().rstrip()))
def S(): return sys.stdin.readline().rstrip()
def LS(): return list(sys.stdin.readline().rstrip().split())
def LS2(): return list(sys.stdin.readline().rstrip())


K = I()
E = [(0,0)]*(K+6)
# E[i] = サイコロの目の合計がiのときのサイコロの振る回数の期待値
# (a,b) ⇔ a+b*E[0]
for i in range(K+1,K+6):
    E[i] = (0,1)

for i in range(K-1,-1,-1):
    a,b = 0,0
    for j in range(i+1,i+7):
        c,d = E[j]
        a += c
        b += d
    E[i] = 1+a/6,b/6

a,b = E[0]
ans = a/(1-b)
print(ans)