#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m, pos, num;
  scanf("%d %d", &n, &m);
  vector<int> s(n + 1, -1);
  bool ex = 0;
  for (int i = 0; i < m; i++) {
    scanf("%d %d", &pos, &num);
    pos--;
    if ((s[pos] > -1 && s[pos] != num) || (pos + num < 0 && n > 1)) {
      return cout << -1 << endl, 0;
    }
    s[pos] = num;
  }
  cout << (s[0] == -1 ? (n > 1 ? 1 : 0) : s[0]);
  for (int i = 1; i < n; i++) cout << max(s[i], 0);
  cout << endl;
}
