output_description: Print the integer K satisfying the condition.
  
  If such an integer does not exist, print `IMPOSSIBLE` instead.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      A B
attempt: k = int(input())
  x, y = [int(x) for x in input().strip().split(" ")]
  x, y = x - y, x + y
  
  
  def main():
      if k % 2 == 0:
          if x % 2 != 0:
              return -1
      return to(x, y)
  
  
  def cc(x, xs):
      if abs(x - xs) <= 2 * k:
          if abs(x + k - xs) % 2 == k % 2:
              if abs(x + k - xs) <= abs(x - k - xs):
                  xs = x + k
              else:
                  xs = x - k
              return (True, xs)
          else:
              if x > xs:
                  xs += k
              else:
                  xs -= k
      else:
          if x > xs:
              xs += k
          else:
              xs -= k
      return (False, xs)
  
  
  def to(x, y):
      rs = []
      xs, ys = 0, 0
      while True:
          if abs(x - xs) == k or abs(y - ys) == k:
              if abs(x - xs) <= k and abs(y - ys) <= k:
                  return rs + [(x, y)]
          mm, ys = cc(y, ys)
          if mm:
              if x > xs:
                  xs += k
              else:
                  xs -= k
          else:
              mm, xs = cc(x, xs)
          rs.append((xs, ys))
  
  
  if __name__ == "__main__":
      jj = main()
      if jj == -1:
          print(-1)
      else:
          print(len(jj))
          for r in jj:
              print((r[0] + r[1]) // 2, (r[1] - r[0]) // 2)
  
problem_description: Statement
  
  We have two distinct integers A and B.
  
  Print the integer K such that |A - K| = |B - K|.
  
  If such an integer does not exist, print `IMPOSSIBLE` instead.
samples: [{"input": "2 16", "output": "9\n    \n\n|2 - 9| = 7 and |16 - 9| = 7, so 9 satisfies the condition.\n\n* * *"}, {"input": "0 3", "output": "IMPOSSIBLE\n    \n\nNo integer satisfies the condition.\n\n* * *"}, {"input": "998244353 99824435", "output": "549034394"}]