output_description: Print a positive integer not greater than 10^{18} that is a multiple of X but
  not a multiple of Y, or print -1 if it does not exist.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      X Y
attempt: 
  x, y =  map(int, input().split())
  i = 1
  if x % y == 0;
      print(-1)
  else:
      for i in range(10 ** 18 + 1):
          if (i * x) % y != 0:
              print(i * x)
              break
          else:
              continue
  
problem_description: Statement
  
  You are given positive integers X and Y. If there exists a positive integer
  not greater than 10^{18} that is a multiple of X but not a multiple of Y,
  choose one such integer and print it. If it does not exist, print -1.
samples: [{"input": "8 6", "output": "16\n    \n\nFor example, 16 is a multiple of 8 but not a multiple of 6.\n\n* * *"}, {"input": "3 3", "output": "-1\n    \n\nA multiple of 3 is a multiple of 3."}]