#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m, y, z;
  cin >> n >> m;
  vector<int> x(n, 0);
  for (int i = 0; i < m; i++) {
    cin >> y >> z;
    if (y < 1 || n < y) {
      cout << -1 << endl;
      exit(0);
    }
    if (x[y] != 0 && x[y] != z) {
      cout << -1 << endl;
      exit(0);
    }
    if (z == 0) {
      if (y == 1) {
        cout << -1 << endl;
        exit(0);
      } else {
        z = 10;
      }
    }
    x[y] = z;
  }
  if (x[1] == 0) x[1] = 1;
  for (int i = 1; i < n + 1; i++) {
    cout << x[i] % 10;
  }
  cout << endl;
}
