#include <bits/stdc++.h>
using namespace std;
int main() {
  int t;
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int n, m;
  cin >> n >> m;
  int arr[n];
  for (int i = 0; i < n; i++) {
    arr[i] = -1;
  }
  int s;
  int v;
  for (int i = 0; i < m; i++) {
    cin >> s >> v;
    if (arr[s - 1] == -1 || arr[s - 1] == v)
      arr[s - 1] = v;
    else {
      if (arr[s - 1] != v) {
        cout << -1 << endl;
        return 0;
      }
    }
  }
  if (n > 1 && arr[0] == 0) {
    cout << -1 << endl;
    return 0;
  }
  if (arr[0] == -1) arr[0] = 1;
  if (arr[1] == -1) arr[1] = 0;
  if (arr[2] == -1) arr[2] = 0;
  for (int i = 0; i < n; i++) cout << arr[i];
  cout << endl;
}
