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