#include <bits/stdc++.h>
using namespace std;
int main() {
  int N, M;
  cin >> N >> M;
  vector<int> s(M), c(M);
  for (int i = 0; i < M; i++) cin >> s[i] >> c[i];
  if (N == 1) {
    for (int i = 1; i < M; i++) {
      if (c[i] != c[0]) {
        cout << -1 << endl;
        return 0;
      }
    }
    cout << c[0] << endl;
    return 0;
  }
  vector<int> ans(N, -1);
  for (int i = 0; i < M; i++) {
    if (ans[s[i] - 1] == -1)
      ans[s[i] - 1] = c[i];
    else {
      if (ans[s[i] - 1] != c[i]) {
        cout << -1 << endl;
        return 0;
      }
    }
  }
  for (int i = 0; i < N; i++) {
    if (ans[i] == -1) {
      if (i == 0)
        ans[i] = 1;
      else
        ans[i] = 0;
    }
    if (ans[0] == 0) {
      cout << -1 << endl;
      return 0;
    }
    cout << ans[i];
  }
  cout << endl;
  return 0;
}
