import sys
N,M = map(int,input().split())
res = ['a' for _ in range(N)]
for i in range(M):
  s,c = map(int,input().split())
  if res[s-1] != 'a' and res[s-1] != str(c):
    print('-1')
    sys.exit(0)
  else:
    res[s-1] = str(c)
for i in range(N):
    if res[i] == 'a':
        if i == 0:
            res[i] = '1'
        else:
            res[i] = '0'
st = ''
for i in range(N):
  st += res[i]
if st[0] == '0' and len(st) > 1:
  print(-1)
  sys.exit(0)
print(st)