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

int main(){
  int a[5];
  a[0] = -1;
  a[1] = -1;
  a[2] = -1;
  int n,m;
  cin >> n >> m;
  int s,c;
  for(int i=0; i<m; i++){
    cin >> s >> c;
    if(a[n-s] == -1){
      a[n-s] = c;
    } else if(a[n-s] != c){
      cout << -1;
      return 0;
    }
  }
  if(n>=2 && a[n-1] == 0){
    cout << -1;
    return 0;
  } else if(n>=2 && a[n-1] == -1){
    a[n-1] = 1;
  }
  cout << max(a[0],0)+max(a[1],0)*10+max(a[2],0)*100;
}
