output_description: Print the abbreviation for the N-th round of ABC.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N
attempt: d = {}
  n, m = map(int, input().split())
  for _ in range(m):
      i, j = map(int, input().split())
      if j in d:
          d[j].append(i)
      else:
          d[j] = [i]
  flag = 0
  if n in d:
      for item in d[n]:
          if item in d and 1 in d[item]:
              flag = 1
              break
  print("POSSIBLE" if flag else "IMPOSSIBLE")
  
problem_description: Statement
  
  This contest, _AtCoder Beginner Contest_ , is abbreviated as _ABC_.
  
  When we refer to a specific round of ABC, a three-digit number is appended
  after ABC. For example, ABC680 is the 680th round of ABC.
  
  What is the abbreviation for the N-th round of ABC? Write a program to output
  the answer.
samples: [{"input": "100", "output": "ABC100\n    \n\nThe 100th round of ABC is ABC100.\n\n* * *"}, {"input": "425", "output": "ABC425\n    \n\n* * *"}, {"input": "999", "output": "ABC999"}]