#include <bits/stdc++.h>
using namespace std;
int main() {
  int N, M;
  cin >> N >> M;
  int S[N];
  for (int i = 0; i < N; i++) S[i] = -1;
  for (int i = 0; i < M; i++) {
    int s, c;
    cin >> s >> c;
    if (s == 1 && c == 0) {
      cout << -1;
      return 0;
    }
    if (S[s - 1] == -1) {
      S[s - 1] = c;
    } else if (S[s - 1] != c) {
      cout << -1;
      return 0;
    }
  }
  cout << ((S[0] == -1) ? 1 : S[0]);
  for (int i = 1; i < N; i++) {
    cout << ((S[i] == -1) ? 0 : S[i]);
  }
  return 0;
}
