#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  int num[3];
  for (int i = 0; i < 3; i++) num[i] = -1;
  cin >> n >> m;
  bool f = true;
  int s, c;
  for (int i = 0; i < m; i++) {
    cin >> s >> c;
    if (num[s - 1] != -1 && c != num[s - 1]) {
      f = false;
    }
    num[s - 1] = c;
  }
  if (num[0] == -1 && n > 1) num[0] = 1;
  if (num[0] == -1 && n == 1) num[0] = 0;
  for (int i = 1; i < 3; i++) {
    if (num[i] == -1) num[i] = 0;
  }
  if (f == false)
    cout << -1 << endl;
  else {
    for (int i = 0; i < n; i++) cout << num[i];
    cout << endl;
  }
}
