#include <bits/stdc++.h>
int main() {
  int n, m;
  std::cin >> n >> m;
  std::vector<int> a(n, -1);
  for (int i = 0; i < m; i++) {
    int s, c;
    std::cin >> s >> c;
    s--;
    if (a.at(s) != -1 && a.at(s) != c || s == 0 && c == 0) {
      std::cout << -1 << std::endl;
      return 0;
    }
    a.at(s) = c;
  }
  for (int i = 0; i < n; i++) {
    std::cout << (a.at(i) == -1 ? (i == 0 ? 1 : 0) : a.at(i));
  }
  std::cout << std::endl;
}
