#include <bits/stdc++.h>
using namespace std;
int a[5] = {}, vis[5] = {};
int n, m;
int main() {
  cin >> n >> m;
  for (int i = 1; i <= m; i++) {
    int p, x;
    cin >> p >> x;
    if (vis[p] && a[p] != x) {
      cout << -1 << '\n';
      return 0;
    }
    if (p == 1 && x == 0) {
      cout << -1 << '\n';
      return 0;
    }
    vis[p] = 1;
    a[p] = x;
  }
  if (!vis[1] && n != 1) a[1] = 1;
  for (int i = 1; i <= n; i++) cout << a[i];
  cout << '\n';
  return 0;
}
