#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  cin >> n >> m;
  int arr[n + 1];
  for (int i = 0; i <= n; i++) arr[i] = -1;
  bool hit = true;
  for (int i = 0; i < m; i++) {
    int x, c;
    cin >> x >> c;
    if (arr[x] == -1) {
      arr[x] = c;
    } else {
      hit = false;
      break;
    }
  }
  if (hit) {
    if (arr[1] == -1) arr[1] = 1;
    for (int i = 1; i <= n; i++) {
      if (arr[i] == -1)
        cout << 0;
      else
        cout << arr[i];
    }
  } else
    cout << -1;
}
