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