#include <bits/stdc++.h>
using namespace std;
void solve() {
  long long int n, m, i, p, d;
  cin >> n >> m;
  long long int A[n];
  for (i = 0; i < n; i++) A[i] = -1;
  for (i = 0; i < m; i++) {
    cin >> p >> d;
    if (A[p - 1] == -1 || A[p - 1] == d)
      A[p - 1] = d;
    else {
      cout << "-1\n";
      return;
    }
  }
  if (n > 1 && A[0] == 0)
    cout << "-1\n";
  else {
    if (A[0] == -1) A[0] = 1;
    for (i = 1; i < n; i++) {
      if (A[i] == -1) A[i] = 0;
    }
    for (i = 0; i < n; i++) cout << A[i];
    cout << "\n";
  }
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  solve();
  return 0;
}
