#include <bits/stdc++.h>
using namespace std;
multiset<pair<string, int> > mul;
int main() {
  string ss;
  int k;
  cin >> ss >> k;
  for (int i = 0; i < ss.size(); i++) {
    string temp;
    temp += ss[i];
    mul.insert({temp, i});
  }
  long long n = ss.size();
  if (2 * k > n * (n + 1)) {
    cout << "No such line." << endl;
  } else {
    pair<string, int> p, ans;
    while (k--) {
      ans = p = *mul.begin();
      mul.erase(mul.begin());
      if (p.second + 1 < n) {
        p.first += ss[p.second + 1];
        p.second += 1;
        mul.insert(p);
      }
    }
    cout << ans.first << endl;
  }
  return 0;
}
