o = input().split()
ans = ""
r = ["e" for i in range(int(o[0]))]
for i in range(int(o[1])):
  p = input().split()
  if r[int(p[0])-1] != "e" and r[int(p[0])-1] != p[1]:
    ans = "-1"
    break
  r[int(p[0])-1] = p[1]
if ans != "-1":
  if r[0] == "0":
    ans = "-1"
  else:
    res =  ""
    for i in range(len(r)):
      res = res + str(r[i])
    if res.replace("e", "0").lstrip("0") == "":
      ans = "0"
    elif res[0] == "e":
      res = res.replace("e", "0")
      temp = list(res)
      temp[0] = "1"
      ans = "".join(temp)
    else:
      ans = res.replace("e", "0")

print(ans)