n, m = map(int, input().split())
s = []
c = []
for i in range(n):
  S, C = map(int, input().split())
  s.append(S)
  c.append(C)
for i in range(10 **(n + 1)):
  tmp = str(i)
  if len(tmp) == n and all([tmp[s[j] - 1] == str(c[j]) for j in range(m)]):
    print(tmp)
    exit()
print(-1)