#include <bits/stdc++.h>
using namespace std;
int n, m, a[10], b[10];
int s, c;
int main() {
  cin >> n >> m;
  for (int i = 1; i <= 5; i++) a[i] = -1;
  for (int i = 1; i <= m; i++) {
    cin >> s >> c;
    if (s == 1 && c == 0) n = -1;
    if (a[s] != -1 && a[s] != c) n = -1;
    a[s] = c;
  }
  if (n == -1) {
    cout << -1 << endl;
    return 0;
  }
  if (a[1] == -1) a[1] = 1;
  for (int i = 1; i <= n; i++) {
    if (a[i] == -1) a[i] = 0;
    cout << a[i];
  }
  cout << endl;
}
