#include <bits/stdc++.h>
using namespace std;
#define rep(i,n) for(int i=0;i<(n);++i)
using ll=long long;
using P pair<int,int>;

int main() {

  int n,m;
  cin>>n>>m;
  vector<P> p(m);
  rep(i,m) cin>>p[i].first>>p[i].second;
  rep(x,1000){
    int keta=1;
    int nx =x/10;
    vector<int> d(1,x%10);
    while(nx){
      keta++;
      d.push_back(nx%10);
      nx/=10;
    }
    if(keta!=n)continue;
    bool ok=true;
    reverse(d.begin(),d.end());
    rep(i,m){
      if(d[p[i].first-1]!=p[i].second)ok=false
    }
    if(ok){
      cout<<x<<endl;
      return 0;
    }
  }
  cout<<-1<<endl;
  return 0;

}
