n,m = map(int,input().split())
if m != 0:
  a = [list(map(int,input().split())) for raw in range(m)]
  b = sorted(a)
  ans = 0
  if int((b[0])[0]) != 1:
    ans += 10**(n-1)
  t = 0
  u = -1
  che = 0
  for hoge in b:
    x = hoge[0]
    y = hoge[1]
    if x == 1 and y == 0:
      che += 1
    if x != t:
      ans += y*(10**(n-x))
    if x == t and y != u:
      che +=1
    t = x
    u = y
  if che == 0 and ans !=0:
    print(ans)
  elif che == 0 and n == 1:
    print(0)
  else:
    print(-1)
else:
  if n == 1:
    print(0)
  else:
    print(10**(n-1))