#include <bits/stdc++.h>
using namespace std;
template <class T>
inline bool chmax(T &a, const T &b) {
  return b > a ? a = b, true : false;
}
template <class T>
inline bool chmin(T &a, const T &b) {
  return b < a ? a = b, true : false;
}
template <class T>
using MaxHeap = priority_queue<T>;
template <class T>
using MinHeap = priority_queue<T, vector<T>, greater<T>>;
template <class T, class F = less<T>>
void sort_uniq(vector<T> &v, F f = F()) {
  sort(begin(v), end(v), f);
  v.resize(unique(begin(v), end(v)) - begin(v));
}
int d[3];
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  int n, m;
  cin >> n >> m;
  d[0] = d[1] = d[2] = -1;
  for (int i = 0; i < (int)(m); i++) {
    int s, c;
    cin >> s >> c;
    s--;
    if (d[s] != -1 && c != d[s]) {
      cout << -1 << endl;
      exit(0);
    } else if (n > 1 && s == 0 && c == 0) {
      cout << -1 << endl;
      exit(0);
    } else {
      d[s] = c;
    }
  }
  for (int i = 0; i < n; i++) {
    cout << (d[i] == -1 ? 0 : d[i]);
  }
  cout << endl;
  return 0;
}
