#include <bits/stdc++.h>
using namespace std;
int main() {
  int N, M;
  cin >> N >> M;
  vector<int> s_al(N, -1);
  int s, c;
  for (int i = 0; i < M; i++) {
    cin >> s >> c;
    if (s_al[s - 1] != -1 && s_al[s - 1] != c) {
      cout << "-1" << endl;
      return 0;
    } else if (s == 0 && c == 0) {
      cout << "-1" << endl;
      return 0;
    } else {
      s_al[s - 1] = c;
    }
  }
  for (int i = 0; i < N; i++) {
    if (s_al[i] == -1 && i == 0) s_al[i] = 1;
    if (s_al[i] == -1 && i != 0) s_al[i] = 0;
  }
  reverse(s_al.begin(), s_al.end());
  int ans = 0;
  for (int i = 0; i < N; i++) {
    ans += s_al[i] * pow(10, i);
  }
  cout << ans << endl;
}
