#include <bits/stdc++.h>
using namespace std;
template <typename T>
void drop(const T &x) {
  cout << x << '\n';
  exit(0);
}
void solve() {
  int n, m;
  cin >> n >> m;
  vector<int> x(m, -1);
  for (int i = 0; i < m; ++i) {
    int s, c;
    cin >> s >> c;
    if (x[s - 1] == -1 || x[s - 1] == c) {
      x[s - 1] = c;
    } else
      drop(-1);
  }
  if (n != 1 && x[0] == 0) drop(-1);
  for (int i = 1; i < n; ++i) {
    if (x[i] == -1) x[i] = 0;
  }
  if (x[0] == -1 && n >= 2)
    x[0] = 1;
  else if (x[0] == -1)
    x[0] = 0;
  for (int i = 0; i < n; ++i) cout << x[i];
  cout << '\n';
  return;
}
signed main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int T = 1;
  while (T--) solve();
  return 0;
}
