#include <bits/stdc++.h>
using namespace std;
const int nax = 1100;
const long long INF = 1e18 + 2;
void add(long long &a, long long b) {
  a += b;
  a = min(a, INF);
}
int n, m;
long long k;
char s[nax];
vector<string> v;
long long dp[nax][nax];
long long dp2[nax][nax];
long long solve(string t) {
  for (int i = 0; i <= n; ++i)
    for (int j = 0; j <= m; ++j) dp[i][j] = dp2[i][j] = 0;
  int sz = (int)t.size();
  t = '#' + t;
  dp[0][0] = 1;
  for (int i = 0; i <= n - 1; ++i) {
    int len = 0;
    while (len <= sz && i + 1 + len <= n && s[i + 1 + len] == t[1 + len]) len++;
    len++;
    if (len <= sz && len <= n) {
      if (s[i + len] > t[len])
        for (int j = 0; j <= m; ++j) {
          add(dp[i + len][j + 1], dp[i][j]);
          add(dp2[i + len][j + 1], dp[i][j]);
        }
    } else if (len == sz + 1) {
      for (int j = 0; j <= m; ++j) {
        add(dp[i + len - 1][j + 1], dp[i][j]);
        add(dp2[i + len - 1][j + 1], dp[i][j]);
      }
    }
    for (int j = 1; j <= m; ++j) {
      add(dp[i + 1][j], dp2[i][j]);
      add(dp2[i + 1][j], dp2[i][j]);
    }
  }
  return dp[n][m];
}
int main() {
  scanf("%d%d%lld", &n, &m, &k);
  scanf("%s", s + 1);
  for (int i = 1; i <= n; ++i) {
    string w = "";
    for (int j = i; j <= n; ++j) {
      w.push_back(s[j]);
      v.push_back(w);
    }
  }
  sort(v.begin(), v.end());
  int l = 0, r = (int)v.size() - 1;
  while (l < r) {
    int m = (l + r + 1) / 2;
    if (solve(v[m]) < k)
      r = m - 1;
    else
      l = m;
  }
  cout << v[l];
  return 0;
}
