def main():
    n,m=map(int,input().split())
    ls=[list(map(int,input().split())) for i in range(m)]
    ans=[-1]*n
    
    flag=True
    for i in ls:
        idx,value=i[0]-1,i[1]
        tgt=ans[idx]
        if tgt!=value and tgt!=-1:
            flag=False
            break
        else:
            ans[idx]=i[1]
    
    if flag:
        if ans[0]==0:
            if n==1:
                print(0)
            else:
                print(-1)
        else:
            for i in range(n):
                if ans[i]==-1:
                    if i == 0:
                        ans[i]=1
                    else:
                        ans[i]=0
            print(int("".join(list(map(str,ans)))))
    else:
        print(-1)
main()