#graph implementation
import math
n,m=map(int,input().split())
ans=['l']*n
flag=False
for i in range(m):
    s,c=map(int,input().split())
    if ans[s-1]=='l':
      ans[s-1]=c
    else:
        if ans[s-1]!=c:
            print(-1)
            exit(0)
    if s-1==0:
        flag=True
#print(ans)
if not flag:
    ans[0]=1
for i in range(n):
    if ans[i]=='l':
        ans[i]=0
if ans[0]==0 and n>1:
    print(-1)
else:
    for i in ans:
        print(i,end="")
print()
