#include <bits/stdc++.h>
using namespace std;
using ll = long long;
int main() {
  int n, m;
  cin >> n >> m;
  vector<vector<int>> data(m, vector<int>(2));
  for (int i = 0; i < m; i++) {
    for (int j = 0; j < 2; j++) {
      cin >> data.at(i).at(j);
    }
  }
  for (int i = 0; i < m; i++) {
    for (int j = 0; j < m - i; j++) {
      if (data.at(i).at(0) == data.at(i + j).at(0) &&
          data.at(i).at(1) != data.at(i + j).at(1)) {
        cout << -1 << endl;
        return 0;
      }
      if (n > 1 && data.at(i).at(0) == 1 && data.at(i).at(1) == 0) {
        cout << -1 << endl;
        return 0;
      }
    }
  }
  int one = 0;
  int two = 0;
  int thr = 0;
  for (int i = 0; i < m; i++) {
    if (data.at(i).at(0) == 1) one = (data.at(i).at(1)) * pow(10, n - 1);
    if (data.at(i).at(0) == 2) two = (data.at(i).at(1)) * pow(10, n - 2);
    if (data.at(i).at(0) == 3) thr = (data.at(i).at(1));
  }
  cout << one + two + thr << endl;
}
