import sys
n,m=list(map(int,input().split()))
ans=[-1 for i in range(n)]

for i in range(m):
  s,c=list(map(int,input().split()))
  if n!=1 and s==1 and c==0:
    print(-1)
    sys.exit()
  if ans[s-1]==-1 or ans[s-1]==c:
    ans[s-1]=c
  else:
    print(-1)
    sys.exit()

    
if n==1 and ans[0]==0:
  print(0)
  sys.exit()
if ans[0]==-1:
  ans[0]=1
for i in range(1,n):
  if ans[i]==-1:
    ans[i]=0
ans=map(str, ans)
print("".join(ans))

  