output_description: Print the N-th Lucas number.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N
attempt: import sys
  
  input = lambda: sys.stdin.readline().rstrip()
  sys.setrecursionlimit(10**7)
  INF = 10**20
  
  
  def I():
      return int(input())
  
  
  def F():
      return float(input())
  
  
  def S():
      return input()
  
  
  def LI():
      return [int(x) for x in input().split()]
  
  
  def LI_():
      return [int(x) - 1 for x in input().split()]
  
  
  def LF():
      return [float(x) for x in input().split()]
  
  
  def LS():
      return input().split()
  
  
  def resolve():
      N = I()
  
      lucas = [0] * (N + 1)
      lucas[0] = 2
      lucas[1] = 1
      for i in range(N - 1):
          lucas[i + 2] = lucas[i] + lucas[i + 1]
  
      print(lucas[-1])
  
  
  if __name__ == "__main__":
      resolve()
  
problem_description: Statement
  
  It is November 18 now in Japan. By the way, 11 and 18 are adjacent Lucas
  numbers.
  
  You are given an integer N. Find the N-th Lucas number.
  
  Here, the i-th Lucas number L_i is defined as follows:
  
    * L_0=2
    * L_1=1
    * L_i=L_{i-1}+L_{i-2} (i≥2)
samples: [{"input": "5", "output": "11\n    \n\n  * L_0=2\n  * L_1=1\n  * L_2=L_0+L_1=3\n  * L_3=L_1+L_2=4\n  * L_4=L_2+L_3=7\n  * L_5=L_3+L_4=11\n\nThus, the 5-th Lucas number is 11.\n\n* * *"}, {"input": "86", "output": "939587134549734843"}]