#include <bits/stdc++.h>
using namespace std;
int main() {
  int N, M;
  int i;
  int t, u;
  cin >> N >> M;
  vector<int> num(N);
  for (i = 0; i < M; ++i) {
    cin >> t >> u;
    if (t == 1 && u == 0) {
      cout << -1 << endl;
      return 0;
    }
    if (num.at(t - 1) == 0 || num.at(t - 1) == u) {
      num.at(t - 1) = u;
    } else {
      cout << -1 << endl;
      return 0;
    }
  }
  if (num.at(0) == 0) {
    num.at(0) = 1;
  }
  for (i = 0; i < N; ++i) {
    cout << num.at(i);
  }
  cout << endl;
}
