#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  cin >> n >> m;
  int s[m], c[m];
  for (int i = 0; i < m; i++) cin >> s[i] >> c[i];
  for (int i = 0; i < 1000; i++) {
    string str = to_string(i);
    int cnt = 0;
    for (int j = 0; j < m; j++) {
      if (str[s[j] - 1] - '0' == c[j]) cnt++;
    }
    if (cnt == m) {
      cout << i << endl;
      return 0;
    }
  }
  cout << "-1" << endl;
  return 0;
}
