#include <bits/stdc++.h>
using namespace std;
typedef long long  ll;
int main(){
  int n,m;
  cin>>n>>m;
  vector<int> s(n);
  bool ok = true;
  for(int i=0; i<m; i++){
    int tmp1, tmp2;
    cin>>tmp1>>tmp2;
    if(s.at(tmp1-1)!=0&&s.at(tmp1-1)!=tmp2) ok =false;
    else s.at(tmp1-1) =tmp2;
    if(tmp1==1&&tmp2==0&&n>1) ok = false;
  }
  if(ok&&s.at(0)==0&&n>1) s.at(0)=1;
  if( ok ){
    for(int i =0; i<n; i++){
      cout<<s.at(i);
    }
    cout<<endl;
  }
  else cout<<-1<<endl;
}
