#include <bits/stdc++.h>
using namespace std;
using ll = long long;
template <class T, class U>
using P = pair<T, U>;
template <class T>
using Heap = priority_queue<T>;
template <class T>
using heaP = priority_queue<T, vector<T>, greater<T>>;
template <class T, class U>
using umap = unordered_map<T, U>;
template <class T>
using uset = unordered_set<T>;
template <class T>
bool ChangeMax(T& a, const T& b) {
  if (a >= b) return false;
  a = b;
  return true;
}
template <class T>
bool ChangeMin(T& a, const T& b) {
  if (a <= b) return false;
  a = b;
  return true;
}
template <class T, size_t N, class U>
void Fill(T (&a)[N], const U& v) {
  fill((U*)a, (U*)(a + N), v);
}
template <class T>
istream& operator>>(istream& is, vector<T>& v) {
  for (auto& e : v) is >> e;
  return is;
}
int main() {
  int n, m;
  cin >> n >> m;
  vector<int> v(10, -1);
  for (int i = 0; i < m; ++i) {
    int x, y;
    cin >> x >> y;
    if (v[x] != -1 && v[x] != y) {
      cout << -1 << endl;
      return 0;
    }
    v[x] = y;
  }
  if (n != 1 && v[1] == 0) {
    cout << -1 << endl;
    return 0;
  }
  for (int i = 0; i < n; ++i) {
    if (v[i + 1] == -1)
      cout << 0;
    else
      cout << v[i + 1];
  }
  cout << endl;
  return 0;
}
