#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  cin >> n >> m;
  bool check = true;
  int s, c, a[5] = {0, -1, -1, -1};
  for (int i = 0; i < m; i++) {
    cin >> s >> c;
    if (a[s] != -1 && a[s] != c)
      check = false;
    else
      a[s] = c;
  }
  if (a[1] == 0) check = false;
  if (check) {
    if (a[1] == -1 && n == 1)
      a[1] = 0;
    else if (a[1] == -1)
      a[1] = 1;
    for (int i = 1; i <= n; i++) {
      if (a[i] == -1) a[i] = 0;
      cout << a[i];
    }
  } else
    cout << -1;
  return 0;
}
