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: n, a, b = map(int, input().split())
  if n * a <= b:
      print(n * a)
  elif n * a >= b:
      print(b)
  
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"}]