#include <bits/stdc++.h>
using namespace std;
using P = pair<long long, long long>;
using WeightedGraph = vector<vector<P>>;
using UnWeightedGraph = vector<vector<long long>>;
const long long INF = 1LL << 60;
const long long MOD = 1000000007;
template <class T>
inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T>
inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <typename T, typename U>
istream &operator>>(istream &is, pair<T, U> &p_var) {
  is >> p_var.first >> p_var.second;
  return is;
}
template <typename T>
istream &operator>>(istream &is, vector<T> &vec) {
  for (T &x : vec) is >> x;
  return is;
}
template <typename T>
istream &operator>>(istream &is, vector<vector<T>> &df) {
  for (long long i = 0; i < df.size(); i++)
    for (long long j = 0; j < df[i].size(); j++) is >> df[i][j];
  return is;
}
template <typename T, typename U>
ostream &operator<<(ostream &os, pair<T, U> &pair_var) {
  cerr << '{';
  os << pair_var.first;
  cerr << ',';
  os << " " << pair_var.second;
  cerr << '}';
  return os;
}
template <typename T>
ostream &operator<<(ostream &os, vector<T> &vec) {
  cerr << '[';
  for (long long i = 0; i < vec.size(); i++)
    os << vec[i] << (i + 1 == vec.size() ? "" : " ");
  cerr << ']';
  return os;
}
template <typename T>
ostream &operator<<(ostream &os, vector<vector<T>> &df) {
  for (auto &vec : df) os << vec;
  return os;
}
template <typename T, typename U>
ostream &operator<<(ostream &os, map<T, U> &map_var) {
  cerr << "{";
  for (auto itr = map_var.begin(); itr != map_var.end(); itr++) {
    os << *itr;
    itr++;
    if (itr != map_var.end()) cerr << ", ";
    itr--;
  }
  cerr << "}";
  return os;
}
template <typename T>
ostream &operator<<(ostream &os, set<T> &set_var) {
  cerr << "{";
  for (auto itr = set_var.begin(); itr != set_var.end(); itr++) {
    os << *itr;
    itr++;
    if (itr != set_var.end()) cerr << ", ";
    itr--;
  }
  cerr << "}";
  return os;
}
void print() { cout << endl; }
template <class Head, class... Tail>
void print(Head &&head, Tail &&...tail) {
  cout << head;
  if (sizeof...(tail) != 0) cout << " ";
  print(forward<Tail>(tail)...);
}
void dump_func() { cerr << '#' << endl; }
template <typename Head, typename... Tail>
void dump_func(Head &&head, Tail &&...tail) {
  cerr << head;
  if (sizeof...(Tail) > 0) cerr << ", ";
  dump_func(std::move(tail)...);
}
signed main(void) {
  cin.tie(0);
  ios::sync_with_stdio(false);
  long long n, m;
  cin >> n >> m;
  string s = "";
  for (long long(i) = 0; (i) < (n); (i)++) s += "?";
  if (n == 1) {
    vector<pair<long long, long long>> p(m);
    cin >> p;
    sort(p.begin(), p.end());
    p.erase(unique(p.begin(), p.end()), p.end());
    if (p.size() == 1) {
      print(p[0].second);
    } else {
      print(-1);
    }
    return 0;
  }
  for (long long(i) = 0; (i) < (m); (i)++) {
    long long x, d;
    cin >> x >> d;
    char num = '0' + d;
    x--;
    if (x == 0 && num == '0') {
      print(-1);
      return 0;
    }
    if (s[x] == '?') {
      s[x] = num;
    } else {
      if (s[x] != num) {
        print(-1);
        return 0;
      }
    }
  }
  if (s[0] == '?') s[0] = '1';
  for (long long(i) = 0; (i) < (s.size()); (i)++) {
    if (i == 0) continue;
    if (s[i] == '?') s[i] = '0';
  }
  print(s);
}
