#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  cin >> n >> m;
  string r(n, 'a');
  for (int i = 0; i < m; i++) {
    int s, c;
    cin >> s >> c;
    if (n != 1 && s == 1 && !c || r[s - 1] != 'a' && r[s - 1] != c + '0') {
      cout << -1 << endl;
      return 0;
    }
    r[s - 1] = c + '0';
  }
  for (int i = 0; i < n; i++)
    if (r[i] == 'a') r[i] = n ? !i + '0' : '0';
  cout << r << endl;
  return 0;
}
