n,m = map(int,input().split())
req = [list(map(int,input().split())) for i in range(m)]

for i in range(10000):
  st = str(i)
  if len(st) != n:
    continue
  ok = True
  for s,c in req:
    if int(st[s-1]) != int(c):
      ok = False
  if ok:
    print(st)
    exit()
    
print(-1)