#include <bits/stdc++.h>
using namespace std;
template <typename T>
using vec = vector<T>;
using lint = long long;
using ulint = unsigned long long;
using pint = pair<int, int>;
using plint = pair<lint, lint>;
template <typename S, typename T>
ostream& operator<<(ostream& os, pair<S, T> p) {
  os << "(";
  os << p.first << ", " << p.second;
  return os << ")";
}
template <typename T>
ostream& operator<<(ostream& os, vec<T> v) {
  os << "[";
  if (v.size() == 0) return os << "]";
  for (int i = 0; i < v.size() - 1; i++) {
    os << v.at(i) << ", ";
  }
  return os << v.at(v.size() - 1) << "]";
}
template <typename T>
ostream& operator<<(ostream& os, set<T>& s) {
  os << "{";
  if (s.begin() == s.end()) return os << "}";
  auto it_first_item = s.begin();
  os << *it_first_item;
  for (auto it = ++it_first_item; it != s.end(); it++) {
    os << ", " << *it;
  }
  return os << "}";
}
template <typename T>
ostream& operator<<(ostream& os, unordered_set<T>& s) {
  os << "{";
  if (s.begin() == s.end()) return os << "}";
  auto it_first_item = s.begin();
  os << *it_first_item;
  for (auto it = ++it_first_item; it != s.end(); it++) {
    os << ", " << *it;
  }
  return os << "}";
}
template <typename K, typename V>
ostream& operator<<(ostream& os, map<K, V> m) {
  os << "{";
  if (m.begin() == m.end()) return os << "}";
  auto it_first_item = m.begin();
  os << it_first_item->first << ": " << it_first_item->second;
  for (auto it = ++it_first_item; it != m.end(); it++) {
    os << ", " << it->first << ": " << it->second;
  }
  return os << "}";
}
template <typename K, typename V>
ostream& operator<<(ostream& os, unordered_map<K, V> m) {
  os << "{";
  if (m.begin() == m.end()) return os << "}";
  auto it_first_item = m.begin();
  os << it_first_item->first << ": " << it_first_item->second;
  for (auto it = ++it_first_item; it != m.end(); it++) {
    os << ", " << it->first << ": " << it->second;
  }
  return os << "}";
}
lint pow(lint num, lint e, lint MOD) {
  lint res = 1;
  lint cur_num = num;
  while (e) {
    if (e & 1) {
      res *= cur_num;
      res %= MOD;
    }
    cur_num *= cur_num;
    cur_num %= MOD;
    e >>= 1;
  }
  return res;
}
int main() {
  cin.tie(0);
  cout.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(10);
  lint N, M;
  cin >> N >> M;
  string res(N, 'a');
  for (long long int(i) = (0); (i) < (M); (i)++) {
    lint s, c;
    cin >> s >> c;
    s--;
    if (res.at(s) != 'a' and res.at(s) != c + '0') {
      cout << -1 << "\n";
      return 0;
    }
    res.at(s) = c + '0';
  }
  for (long long int(i) = (0); (i) < (N); (i)++)
    if (res.at(i) == 'a') res.at(i) = '0';
  cout << (N > 1 and res.at(0) == '0' ? "-1" : res) << "\n";
}
