k=int(input())

dp=[[0]*(k+1) for i in range(k+1)]
dp[0][0]=1
for i in range(k):
  for j in range(k):
    for j2 in range(1,7):
      dp[i+1][min(j+j2,k)]+=dp[i][j]/6

ans=0
for i in range(k+1):
  ct=0
  for j in range(k+1):
    if j>=k:
      ct+=dp[i][j]
  ans+=ct*i
print(ans)