output_description: Output the greatest common divisor of _a_ and _b_.
input_description: _a_ and _b_ are given in a line sparated by a single space.
attempt: import sys
  
  input = lambda: sys.stdin.readline().rstrip()
  sys.setrecursionlimit(10**7)
  INF = 10**10
  
  
  def I():
      return int(input())
  
  
  def F():
      return float(input())
  
  
  def SS():
      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 LSS():
      return input().split()
  
  
  def resolve():
      x, y = LI()
  
      def gcd(x, y):
          if x < y:
              x, y = y, x
          if x % y == 0:
              return y
          else:
              return gcd(y, x % y)
  
      print(gcd(x, y))
  
  
  if __name__ == "__main__":
      resolve()
  
problem_description: Greatest Common Divisor
  
  Write a program which finds the greatest common divisor of two natural numbers
  _a_ and _b_
samples: [{"input": "54 20", "output": "2"}, {"input": "147 105", "output": "21"}]