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