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: import math
  from math import gcd, pi, sqrt
  
  INF = float("inf")
  
  import sys
  
  sys.setrecursionlimit(10**6)
  import itertools
  from collections import Counter, deque
  
  
  def i_input():
      return int(input())
  
  
  def i_map():
      return map(int, input().split())
  
  
  def i_list():
      return list(i_map())
  
  
  def i_row(N):
      return [i_input() for _ in range(N)]
  
  
  def i_row_list(N):
      return [i_list() for _ in range(N)]
  
  
  def s_input():
      return input()
  
  
  def s_map():
      return input().split()
  
  
  def s_list():
      return list(s_map())
  
  
  def s_row(N):
      return [s_input for _ in range(N)]
  
  
  def s_row_str(N):
      return [s_list() for _ in range(N)]
  
  
  def s_row_list(N):
      return [list(s_input()) for _ in range(N)]
  
  
  import string
  
  
  def main():
      n, m = i_map()
  
      c = [[INF] * n for _ in range(n)]
      for i in range(n):
          c[i][i] = 0
  
      for _ in range(m):
          a, b = i_map()
          c[a - 1][b - 1] = 1
          c[b - 1][a - 1] = 1
  
      for i, k in enumerate(c[0]):
          if k == 1:
              if c[i][-1] == 1:
                  print("POSSIBLE")
                  exit()
      print("IMPOSSIBLE")
  
  
  if __name__ == "__main__":
      main()
  
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"}]