#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  cin >> n >> m;
  int a[4] = {-1, -1, -1, -1};
  int c, s;
  int tmp = 1;
  for (int i = 0; i < m; i++) {
    cin >> s >> c;
    if (a[s] == -1) {
      a[s] = c;
    } else if (a[s] != c)
      tmp = 0;
  }
  if (n == 1 && a[1] == -1)
    cout << 0;
  else {
    if (a[1] == -1) a[1] = 1;
    for (int i = 2; i <= n; i++) {
      if (a[i] == -1) a[i] = 0;
    }
    if (tmp == 0)
      cout << -1;
    else if (a[1] == 0)
      cout << -1;
    else
      for (int i = 1; i <= n; i++) {
        cout << a[i];
      }
  }
  cout << endl;
  return 0;
}
