import sys

n,m = map(int,input().split())
sc = []

if m == 0 and n == 1:
  print(0)
  sys.exit()
elif m == 0 and n != 1:
  print('-1')
  sys.exit()

for _ in range(m):
  sc.append(list(map(int,input().split())))

sc.sort()

if sc[0][0] == 1 and sc[0][1] == 0:
  print('-1')
  sys.exit()

ans = [-1 for _ in range(n)]
for i in range(m):
  if ans[sc[i][0]-1] == -1:
    ans[sc[i][0]-1] = sc[i][1]
  else:
    if ans[sc[i][0]-1] != sc[i][1]:
      print('-1')
      sys.exit()

res = ''
if ans[0] == 0 or ans[0] == -1:
  ans[0] = 1
for i in range(n):
  if ans[i] == -1:
    ans[i] = 0
  res = res + str(ans[i])

print(res)
