#include <bits/stdc++.h>
using namespace std;
using i32 = int_fast32_t;
using i64 = int_fast64_t;
int main() {
  i32 n, m;
  cin >> n >> m;
  vector<i32> v(n), u(n);
  v[0] = 1;
  for (i32 i = 0; i < m; i++) {
    i32 s, c;
    cin >> s >> c, s--;
    if (u[s] && v[s] != c) {
      cout << -1 << endl;
      return 0;
    }
    u[s] = 1;
    v[s] = c;
  }
  if (v[0] == 0) {
    cout << -1 << endl;
    return 0;
  }
  string ans;
  for (auto& e : v) ans.push_back(e + '0');
  cout << ans << endl;
}
