#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  cin >> n >> m;
  vector<int> kazu(n);
  int f = 0;
  int g = 0;
  for (int i = 0; i < m; i++) {
    int a, b;
    cin >> a >> b;
    if (a == 1) {
      g = 1;
    }
    if (kazu.at(a - 1) != 0 && kazu.at(a - 1) != b) {
      f = -1;
    } else {
      kazu.at(a - 1) = b;
    }
  }
  if (g == 0) {
    kazu.at(0) == 1;
  }
  if (f != 0 || (n > 1 && kazu.at(0) == 0)) {
    cout << -1 << endl;
  } else {
    for (int i = 0; i < n; i++) {
      cout << kazu.at(i);
    }
    cout << endl;
  }
}
