#include <bits/stdc++.h>
using namespace std;
const long long inf = 1e18 + 7;
void upd(long long& a, const long long& b) { a = min(a + b, inf); }
const int maxn = 1007, maxm = 1007, abc = 26;
vector<vector<long long> > dp(maxm, vector<long long>(maxn, 0)),
    add(maxm, vector<long long>(maxn, 0));
vector<vector<int> > son(maxn* maxn, vector<int>(abc, -1));
vector<int> p(maxn*maxn, -1), in(maxn*maxn, -1);
vector<char> pv(maxn* maxn, '?');
int n, m, nodes = 1;
string s;
long long k;
void insert_string(int pos) {
  for (int vr = 0; pos < n; vr = son[vr][s[pos] - 'a'], pos++) {
    if (son[vr][s[pos] - 'a'] == -1) {
      son[vr][s[pos] - 'a'] = nodes++;
      in[nodes - 1] = pos;
      p[nodes - 1] = vr;
      pv[nodes - 1] = s[pos];
    }
  }
}
vector<int> ord;
void sort_substrings(int vr) {
  ord.push_back(vr);
  for (int i = 0; i < abc; i++) {
    if (son[vr][i] != -1) sort_substrings(son[vr][i]);
  }
}
long long count_smaller(const string& t) {
  vector<int> pos(n, -1);
  for (int i = 0; i < n; i++) {
    pos[i] = i;
    while (pos[i] < n && pos[i] - i < t.size() && t[pos[i] - i] == s[pos[i]])
      pos[i]++;
    if (pos[i] - i < t.size() && (pos[i] == n || s[pos[i]] < t[pos[i] - i]))
      pos[i] = -1;
    else if (pos[i] - i < t.size())
      pos[i]++;
  }
  for (int i = 0; i <= m; i++)
    for (int j = 0; j <= n; j++) dp[i][j] = add[i][j] = 0;
  dp[0][0] = 1;
  for (int i = 0; i <= m; i++) {
    for (int j = 0; j <= n; j++) {
      if (j) upd(add[i][j], add[i][j - 1]);
      upd(dp[i][j], add[i][j]);
      if (i < m && j < n && pos[j] != -1) upd(add[i + 1][pos[j]], dp[i][j]);
    }
  }
  return dp[m][n];
}
string get_string(int vr) {
  string ans = "";
  while (vr) {
    ans.push_back(pv[vr]);
    vr = p[vr];
  }
  reverse(ans.begin(), ans.end());
  return ans;
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cin >> n >> m >> k >> s;
  for (int i = 0; i < n; i++) insert_string(i);
  sort_substrings(0);
  int lo = 0, hi = ord.size() - 1;
  while (lo < hi) {
    int mid = (lo + hi + 1) >> 1;
    if (count_smaller(get_string(ord[mid])) >= k)
      lo = mid;
    else
      hi = mid - 1;
  }
  cout << get_string(ord[lo]) << "\n";
  return 0;
}
