#include <bits/stdc++.h>
using namespace std;
int main() {
  int N, M;
  int s, c;
  int ans[3];
  bool flag = false;
  cin >> N >> M;
  for (int i = 0; i < 3; i++) ans[i] = -1;
  for (int i = 0; i < M; i++) {
    cin >> s >> c;
    if (ans[s - 1] == -1 || ans[s - 1] == c) {
      ans[s - 1] = c;
    } else {
      flag = true;
    }
  }
  if (flag || ans[0] == 0) {
    cout << "-1" << endl;
    ;
  } else {
    if (ans[0] == -1) {
      if (N == 1) {
        cout << "0" << endl;
        return 0;
      }
      ans[0] = 1;
    }
    for (int i = 1; i < N; i++) {
      if (ans[i] == -1) {
        ans[i] = 0;
      }
      ans[0] = ans[0] * 10 + ans[i];
    }
    cout << ans[0] << endl;
  }
  return 0;
}
