#include <bits/stdc++.h>
using namespace std;
const int N = 1005;
using ll = long long;
const ll INF = LLONG_MAX / 3;
int n, m, lcp[N][N];
ll kk;
char s[N];
ll solve(int l, int r) {
  vector<vector<ll>> dp(2, vector<ll>(n + 2));
  int cur = 0;
  dp[cur][n + 1] = 1;
  for (int i = 1; i <= m; i++) {
    cur ^= 1;
    for (int j = n; j > 0; --j)
      dp[cur ^ 1][j] = min(INF, dp[cur ^ 1][j] + dp[cur ^ 1][j + 1]);
    for (auto &i : dp[cur]) i = 0;
    for (int j = n - i + 1; j > 0; --j) {
      int len = min(r - l + 1, lcp[j][l]);
      if ((len < n - j + 1 ? s[j + len] : -1) <
          (len < r - l + 1 ? s[l + len] : -1))
        continue;
      dp[cur][j] = dp[cur ^ 1][j + len + (len < r - l + 1)];
    }
  }
  return dp[cur][1];
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cin >> n >> m >> kk >> (s + 1);
  for (int i = n; i > 0; --i)
    for (int j = n; j > 0; --j)
      lcp[i][j] = (s[i] == s[j] ? lcp[i + 1][j + 1] + 1 : 0);
  vector<pair<int, int>> sub;
  for (int i = 1; i <= n; i++)
    for (int j = i; j <= n; j++) sub.push_back({i, j});
  sort(sub.begin(), sub.end(), [](pair<int, int> a, pair<int, int> b) -> bool {
    int l1 = a.second - a.first + 1, l2 = b.second - b.first + 1;
    int len = min({lcp[a.first][b.first], l1, l2});
    return (len < l1 ? s[a.first + len] : -1) <
           (len < l2 ? s[b.first + len] : -1);
  });
  int l = 0, r = sub.size() - 1, ans = -1;
  while (l <= r) {
    int mid = (l + r) >> 1;
    if (solve(sub[mid].first, sub[mid].second) >= kk)
      ans = mid, l = mid + 1;
    else
      r = mid - 1;
  }
  for (int i = sub[ans].first; i <= sub[ans].second; i++) cout << s[i];
  return 0;
}
