# import numpy as np
def main():
  N,M =map(int, input().split())
  s,c=[],[]
  for i in range(M):
    si,ci = map(int, input().split())
    s.append(si)
    c.append(ci)
  
  res=['']*N
  for si,ci in zip(s,c):
    if res[si-1]== '':
      res[si-1]=str(ci)	
    elif res[si-1]!= str(ci):
      print(-1)
      exit()
  
  if res[0]=='0':
    print(-1)
    exit()
  elif res[0]=='':
    res[0]=str(1)
   
  for i in range(N):
    if res[i]=='':
      res[i]=str(0)
  print(int("".join(res)))
  
    
if __name__=="__main__":
  main()