N, M=map(int, input().split())
ans=["-1"]*N
f=0
for i in range(M):
  s, c=map(int, input().split())
  if s==1 and c==0:
    f=1
  if ans[s-1]!=str(c) and ans[s-1]!="-1":
    f=1
  ans[s-1]=str(c)

if f==1:
  print(-1)
else:
  if ans[0]=="-1":
    ans[0]="1"
  a="".join(ans)
  b=a.replace("-1", "0")
  print(b)
   