#include <bits/stdc++.h>
using namespace std;
int a[4] = {-1, -1, -1, -1};
int main() {
  int n, m;
  cin >> n >> m;
  for (int i = 0; i < m; i++) {
    int s, c;
    cin >> s >> c;
    if (a[s] != -1 && a[s] != c) {
      cout << -1;
      return 0;
    }
    a[s] = c;
  }
  if (a[1] == 0 && n > 1) {
    cout << -1;
    return 0;
  }
  if (a[1] == -1) a[1] = 1;
  for (int i = 2; i <= n; i++) {
    if (a[i] == -1) {
      a[i] = 0;
    }
  }
  for (int i = 1; i <= n; i++) {
    cout << a[i];
  }
}
