#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m, s[5], c[5], ans[3];
  cin >> n >> m;
  for (int i = 0; i < n; i++) ans[i] = -1;
  for (int i = 0; i < m; i++) {
    cin >> s[i] >> c[i];
  }
  for (int i = 0; i < m; i++) {
    if (ans[s[i] - 1] != -1 && ans[s[i] - 1] != c[i]) {
      cout << -1 << endl;
      return 0;
    }
    ans[s[i] - 1] = c[i];
  }
  if (ans[0] == 0 && n != 0) {
    cout << -1 << endl;
  } else {
    for (int i = 0; i < n; i++) {
      if (ans[i] == -1) {
        if (i == 0) {
          cout << 1;
        } else {
          cout << 0;
        }
      } else {
        cout << ans[i];
      }
    }
  }
  return 0;
}
