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