#include "bits/stdc++.h"
using namespace std;
#define ll long long
#define endl '\n'
#define rep(i, n) for(int i = 0; i < (int)(n); i++)
#define rep2(i,a,b) for(int i=int(a);i<int(b);i++)
#define pb emplace_back
#define all(x) (x).begin(),(x).end()
ll mod=1e9+7;
ll mod2=998244353;
const int INF=1e9;

signed main() {
    ll n,m;
    cin>>n>>m;
    if(m==0){
      if(n==1)cout<<0<<endl;
      if(n==2)cout<<10<<endl;
      if(n==3)cout<<100<<endl;
      return 0;
    }
    string s="";
    rep(i,n)s+="X";
    bool unko=true;
    rep(i,m){
      ll a;
      char b;
      cin>>a>>b;
      a--;
      if(s[a]!='X'&&s[a]!=b)unko=false;
      if(a==0&&b=='0'&&n!=1)unko=false;
      s[a]=b;
    }
    if(s[0]=='X'){
      if(n==1)s[0]='0';
      else s[0]='1';
    }
    if(s[1]=='X')s[1]='0';
    if(s[2]=='X')s[2]='0';
    
    if(unko)cout<<s<<endl;
    else cout<<-1<<endl;
}


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