#include <bits/stdc++.h>
using namespace std;
int s[6], t[6];
int a[3] = {-1, -1, -1};
int main(void) {
  int n, m;
  cin >> n >> m;
  for (int i = 0; i < m; i++) {
    cin >> s[i] >> t[i];
    if (a[s[i] - 1] != -1 && a[s[i] - 1] != t[i]) {
      cout << -1 << endl;
      return 0;
    } else {
      a[s[i] - 1] = t[i];
    }
  }
  if (a[0] == 0 && n != 1) {
    cout << -1 << endl;
    return 0;
  }
  if (n == 1 && m == 0) {
    cout << 1 << endl;
    return 0;
  }
  for (int i = 0; i < n; i++) {
    if (a[i] != -1) {
      cout << a[i];
    } else if (i == 0) {
      cout << 1;
    } else {
      cout << 0;
    }
  }
  cout << endl;
}
