#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  cin >> n >> m;
  vector<int> s(m);
  vector<char> c(m);
  for (int i = 0; i < m; i++) cin >> s[i] >> c[i];
  long long ans = -1;
  if (n == 1) {
    for (int i = pow(10, n - 1) - 1; i < pow(10, n); i++) {
      if (m == 0) {
        int ans = pow(10, n - 1) - 1;
        cout << ans << endl;
        return 0;
      } else {
        string answer = to_string(i);
        for (int j = 0; j < m; j++) {
          if (answer[s[j] - 1] != c[j])
            break;
          else if (j == m - 1) {
            ans = i;
            cout << ans << endl;
            return 0;
          }
        }
      }
      cout << ans << endl;
    }
  }
  if (n != 1) {
    for (int i = pow(10, n - 1); i < pow(10, n); i++) {
      string answer = to_string(i);
      if (m == 0) {
        int ans = pow(10, n - 1);
        cout << ans << endl;
        return 0;
      } else {
        for (int j = 0; j < m; j++) {
          if (answer[s[j] - 1] != c[j])
            break;
          else if (j == m - 1) {
            ans = i;
            cout << ans << endl;
            return 0;
          }
        }
      }
      cout << ans << endl;
    }
  }
}
