#include <bits/stdc++.h>
using namespace std;
const long long mod = 1e9 + 7;
int main() {
  bool check = true;
  int n, m;
  cin >> n >> m;
  int s[10], c[10];
  string st;
  for (int i = 0; i < n; i++) {
    st[i] = 'a';
  }
  for (int i = 0; i < m; i++) {
    cin >> s[i] >> c[i];
    s[i]--;
    if (s[i] == 0 && c[i] == 0) {
      check = false;
    }
    if ((st[s[i]] != 'a') && (st[s[i]] != c[i] + '0')) {
      check = false;
    }
    st[s[i]] = c[i] + '0';
  }
  if (!check) {
    cout << -1 << "\n";
  } else {
    if (st[0] == 'a') {
      cout << '1';
    } else {
      cout << st[0];
    }
    for (int i = 1; i < n; i++) {
      if (st[i] == 'a') {
        cout << 0;
      } else {
        cout << st[i];
      }
    }
    cout << "\n";
  }
}
