#include <bits/stdc++.h>
using namespace std;
int X[3] = {-1, -1, -1};
bool f = true;
int main() {
  int N, M;
  cin >> N >> M;
  while (M--) {
    int A, B;
    cin >> A >> B;
    A--;
    if (!A && !B && N > 1) f = false;
    if (X[A] != -1 && X[A] != B) f = false;
    X[A] = B;
  }
  for (int i = 1; i < N; i++)
    if (X[i] == -1) X[i] = 0;
  if (X[0] == -1 && N > 1) X[0] = 1;
  if (X[0] == -1 && N <= 1)
    if (f) {
      for (int i = 0; i < N; i++) cout << X[i];
    } else
      puts("-1");
  return 0;
}
