n,m=map(int,input().split())
d=["a"]*n
ans=""
if n==1 and m==0:
    print(0)
    exit()
for i in range(m):
    s,c=map(str,input().split())
    if s=="1" and c=="0":
        print(0)
        exit()
    s=int(s)
    if d[s-1]=="a" or d[s-1]==c:
        d[s-1]=c #置き換え
    else:
        ans="-1"
        print(ans)
        break
if d[0]!="0" and ans!="-1":
    if d[0]=="a" or d[0]=="0":
        print("".join(["1"]+d[1:]).replace("a","0"))
    else:
        print(("".join(d)).replace("a","0"))
elif d[0]=="0":
    print(-1)