#include <bits/stdc++.h>
using namespace std;
int main() {
  int m, n;
  cin >> m >> n;
  int a[m + 1];
  int f = 0;
  for (int i = 1; i <= m; i++) {
    a[i] = -1;
  }
  for (int i = 1; i <= n; i++) {
    int x, y;
    cin >> x >> y;
    if (a[x] == -1 || a[x] == y)
      a[x] = y;
    else
      f = 1;
  }
  if (a[1] == 0) f = 1;
  if (a[1] == -1) a[1] = 1;
  if (m == 1 && a[1] == -1) a[1] = 0;
  if (m == 1 && a[1] == 0) f = 0;
  if (f == 1) {
    cout << "-1";
    return 0;
  }
  for (int i = 1; i <= m; i++) {
    if (a[i] == -1) a[i] = 0;
    cout << a[i];
  }
  return 0;
}
