#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  cin >> n >> m;
  vector<int> s(m), c(m);
  for (int i = 0; i < m; i++) cin >> s[i] >> c[i];
  int ans[3];
  ans[0] = -1;
  ans[1] = -1;
  ans[2] = -1;
  for (int i = 0; i < m; i++) ans[s[i] - 1] = c[i];
  for (int i = 0; i < m; i++) {
    if (ans[s[i] - 1] != c[i]) {
      cout << -1 << endl;
      return 0;
    }
  }
  if (n != 1 && ans[0] == 0) {
    cout << -1 << endl;
    return 0;
  }
  if (ans[0] == -1) ans[0] = 1;
  for (int i = 0; i < n; i++)
    if (ans[i] == -1) ans[i] = 0;
  for (int i = 0; i < n; i++) cout << ans[i];
  cout << endl;
  return 0;
}
