#include <bits/stdc++.h>
using namespace std;
int main() {
  int N, M, s[4], c[10];
  cin >> N >> M;
  if (N == 1 && M == 0) {
    cout << 0;
    return 0;
  }
  int fla = 1;
  memset(s, -1, sizeof(s));
  for (int i = 1; i <= M; i++) {
    int ss, cc;
    cin >> ss >> cc;
    if (N > 1 && ss == 1 && cc == 0)
      fla = 0;
    else if (s[ss] == -1)
      s[ss] = cc;
    else {
      if (s[ss] != -1 && s[ss] != cc) fla = 0;
    }
  }
  if (fla == 0) {
    cout << "-1";
    return 0;
  }
  for (int i = 1; i <= N; i++) {
    if (s[i] == -1 && i == 1)
      s[i] = 1;
    else if (s[i] == -1)
      s[i] = 0;
    printf("%d", s[i]);
  }
  return 0;
}
