#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  scanf(" %d %d", &n, &m);
  string ans = "";
  for (int i = 0; i < n; ++i) ans += '*';
  bool posi = 1;
  while (m--) {
    int s, v;
    scanf(" %d %d", &s, &v);
    --s;
    if (ans[s] != '*' && ('0' + v) != ans[s]) {
      posi = 0;
      continue;
    }
    ans[s] = '0' + v;
  }
  if (!posi) {
    puts("-1");
    return 0;
  }
  for (int i = 0; i < n; ++i) {
    if (ans[i] != '*')
      continue;
    else
      ans[i] = (i == 0 ? '1' : '0');
  }
  cout << ans << endl;
  return 0;
}
