#include"bits/stdc++.h"
using namespace std;
using ll=long long;
template<typename T=ll>inline T in(istream&is=cin){T ret;is>>ret;return ret;}
template<typename T>inline auto vec2(typename vector<T>::size_type h,typename vector<T>::size_type w,T v=T()){return vector<vector<T>>(h,vector<T>(w,v));}

int main()
{
    ll n=in(),m=in();
    if(m==0){
        cout<<(n==1?"0":"1"+string(n-1,'0'))<<endl;
    }else{
        string ans(n,'\0');
        for(int i=0;i<m;++i){
            ll s=in()-1;
            char c='0'+in();
            if(ans[s]=='\0'){
                ans[s]=c;
            }else if(ans[s]!=c){
                cout<<-1<<endl;
                return 0;
            }
        }
        if(ans[0]=='0'){
            cout<<-1<<endl;
            return 0;
        }else if(ans[0]=='\0'){
            ans[0]='1';
        }
        for(int i=0;i<n;++i){
            cout<<(ans[i]=='\0'?'0':ans[i]);
        }
        cout<<endl;
    }
}
