#include <bits/stdc++.h>
using namespace std;

int main(){
  int n, m;
  cin >> n >> m;
  vector<pair<int, char>> a(m);
  for(auto& i : a){
    cin >> i.first >> i.second;
    i.first--;
  }
  for(int i = 0; i < 1000; i++){
    string s = to_string(i);
    if(s.size() != n) continue;
    if(any_of(a.begin(), a.end(), [](auto i){ return s[i.first] != i.second; })) continue;
    cout << s << endl;
    return 0;
  }
  cout << -1 << endl;
}