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