N,M = (int(i) for i in input().split())

SC = []
max_digits = 0
for i in range(M):
  S,C = (int(i) for i in input().split())
  SC.append([S,C])
  max_digits = max(max_digits,S)

ans = -1
if M != 0:
  ans = -1
  for i in range(10**(max_digits-1),10**(max_digits)):
    check_flag = True
    for sc in SC:
      s = sc[0]
      c = sc[1]
      if str(i)[s-1] != str(c):
        check_flag = False
        break
    if check_flag is True:
      ans = i
      break
else:
  ans = 0

print(ans)
