#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  cin >> n >> m;
  vector<vector<int> > a(m, vector<int>(2));
  for (int i = 0; i < m; i++) {
    cin >> a[i][0] >> a[i][1];
  }
  for (int i = pow(10, n - 1); i < pow(10, n); i++) {
    string s = to_string(i);
    bool flg = true;
    for (int q = 0; q < m; q++) {
      if (s[a[q][0] - 1] != a[q][1] + '0') {
        flg = false;
        break;
      }
    }
    if (flg == true) {
      cout << s << endl;
      return 0;
    }
  }
  cout << "-1" << endl;
  return 0;
}
