#include <bits/stdc++.h>
using namespace std;
using ll = long long;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  int n, m;
  cin >> n >> m;
  vector<int> num(n, -1);
  int ok = 1;
  for (int i = 0; i < m; i++) {
    int s, c;
    cin >> s >> c;
    s--;
    if (num[s] == -1)
      num[s] = c;
    else if (num[s] != c)
      ok = 0;
  }
  if (num[0] == 0) ok = 0;
  if (!ok) {
    cout << -1 << endl;
  } else {
    for (int i = 0; i < n; i++) {
      if (num[i] == -1) {
        if (i == 0 && n != 1)
          num[i] = 1;
        else
          num[i] = 0;
      }
      cout << num[i];
    }
    cout << endl;
  }
  return 0;
}
