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: x, y = map(int, input().split())
  if x >= y:
      while True:
          a, b = divmod(x, y)
          if b == 0:
              print(y)
              break
          else:
              x = y
              y = b
  elif x < y:
      while True:
          a, b = divmod(y, x)
          if b == 0:
              print(x)
              break
          else:
              y = x
              x = b
  
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"}]