#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  cin >> n >> m;
  if (m == 0) {
    if (n == 1) cout << "0";
    if (n == 2) cout << "10";
    if (n == 3) cout << "100";
  } else {
    vector<int> v(n + 1);
    for (int i = 0; i < n + 1; i++) v[i] = 100;
    int ans = true;
    for (int i = 0; i < m; i++) {
      int key, vlue;
      cin >> key >> vlue;
      if (v[key] == 100)
        v[key] = vlue;
      else if (v[key] != vlue) {
        ans = false;
      }
    }
    if (ans == false)
      cout << "-1";
    else if (v[1] == 0)
      cout << "-1";
    else {
      for (int i = 1; i < n + 1; i++) {
        if (v[i] == 100)
          cout << '0';
        else
          cout << v[i];
      }
    }
  }
  return 0;
}
