#include <bits/stdc++.h>
using namespace std;
int s[3], n, m, a, b;
int main(void) {
  cin >> n >> m;
  for (int i = 0; i < 3; i++) s[i] = -1;
  for (int i = 0; i < m; i++) {
    cin >> a >> b;
    a--;
    if (s[a] != -1 && s[a] != b) {
      cout << -1 << endl;
      return 0;
    }
    s[a] = b;
  }
  if (n != 1 && s[0] == 0) {
    cout << -1 << endl;
    return 0;
  }
  if (s[0] == -1) {
    if (n == 1)
      s[0] = 0;
    else
      s[0] = 1;
  }
  if (s[1] == -1) s[1] = 0;
  if (s[2] == -1) s[2] = 0;
  cout << s[0] << s[1] << s[2] << endl;
}
