N, M = map(int,input().split())
s = []
c = []
for i in range(M):
  S, C = map(int,input().split())
  s.append(S)
  c.append(C)


for i in range(10 ** (N + 1)):
  Str = str(i)

  if len(Str) == N and all([Str[s[j] - 1] == str(c[j]) for j in range(M)]):
      print(Str)
      exit()

print(-1)