#include<bits/stdc++.h>
using namespace std;
int main(){
  int n,m;
  cin>>n>>m;
  map<int,int> mp;
  for(int i = 0; i < m; i++){
  	int si,ci;
    cin>>si>>ci;
    bool f = 0;
    if(mp.count(si)){
    	if(mp[si]!=ci){
        	f = 1;
        }
    }
    mp[si] = ci;  
  }
  if(mp.count(1)){
  	if(mp[1] == 0){
    	f = 1;
    }
  }
  else {
    if( n == 1) mp[1] = 0;
    else
    mp[1] = 1;
  }
  if(f==1){
  	cout<<"-1"<<"\n";
  }
  else{
   for(int i = 1; i <= n; i++){
  	cout<<mp[i];
   }
  }
  return 0;
}