import sys
N, M = map(int, input().split())


sc = dict()
for i in range(M):
  s, c = map(int, input().split())
  if s in sc and sc[s] != c:
    print(-1)
    break
  sc[s] = c
else:
  if N == 1:
    i1 = sc.get(1, -1)
    i2 = -1
    i3 = -1
  elif N == 2:
    i1 = sc.get(2, -1)
    i2 = sc.get(1, -1)
    i3 = -1
  elif N == 3:
    i1 = sc.get(3, -1)
    i2 = sc.get(2, -1)
    i3 = sc.get(1, -1)

  for k in range(0, int(10 ** N)):
    k, k1 = divmod(k, 10)
    k, k2 = divmod(k, 10)
    k, k3 = divmod(k, 10)
    if k == 0 and N == 1 and (i1 == -1 or k1 == i1):
      print(0)
      break
    if (
      (N == 1 and k2 == 0 and k3 == 0 and k1) or
      (N == 2 and k3 == 0 and k2) or
      (N == 3 and k3)
    ):
      if (
        (i1 == -1 or k1 == i1) and
        (i2 == -1 or k2 == i2) and
        (i3 == -1 or k3 == i3)
      ):
        print(int(k3 * 100 + k2 * 10 + k1))
        break
  else:
    print(-1)



