#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cout.tie(0);
  cin.tie(NULL);
  int n, m;
  cin >> n >> m;
  int a[n];
  for (int i = 0; i < n; i++) a[i] = 10;
  while (m--) {
    int s, c;
    cin >> s >> c;
    if (a[s - 1] != 10 && a[s - 1] != c) {
      cout << -1;
      return 0;
    }
    a[s - 1] = c;
    if (a[0] == 0) {
      cout << -1;
      return 0;
    }
  }
  if (a[0] == 10) cout << 1;
  for (int i = 1; i < n; i++) {
    if (a[i] == 10) {
      a[i] = 0;
    }
    cout << a[i];
  }
}
