def main():
  K = int(input())
  dp = [0 for _ in range(K + 10)]
  for i in range(K - 1, -1, -1):
    a = 0
    for j in range(1, 7):
      a += dp[i + j]
    dp[i] = 1 + a / 6
  ans = dp[0]
  print(f"{ans:.10f}")


if __name__ == "__main__":
  main()