#include <bits/stdc++.h>
const long long Infll = 0x3f3f3f3f3f3f3f3f;
const int MN = 1005;
inline void Add(long long &x, long long y) {
  x = (x += y) >= Infll ? Infll : x;
}
long long K;
int N, M, C, lcp[MN][MN];
char str[MN];
struct dat {
  int s, l;
} seq[500505];
long long f[MN], g[MN];
long long Solve(dat now) {
  int st = now.s, len = now.l;
  f[N + 1] = 1;
  for (int i = 1; i <= N; ++i) f[i] = 0;
  for (int t = 1; t <= M; ++t) {
    for (int i = 1; i <= N + 1; ++i) g[i] = 0;
    for (int i = N; i >= 1; --i) Add(f[i], f[i + 1]);
    for (int i = 1; i <= N; ++i) {
      int d = lcp[i][st];
      if (d < len) {
        if (str[i + d] > str[st + d]) g[i] = f[i + d + 1];
      } else
        g[i] = f[i + len];
    }
    std::swap(f, g);
  }
  return f[1];
}
int main() {
  scanf("%d%d%lld%s", &N, &M, &K, str + 1);
  for (int i = N; i >= 1; --i)
    for (int j = N; j >= 1; --j)
      lcp[i][j] = str[i] == str[j] ? lcp[i + 1][j + 1] + 1 : 0;
  for (int i = 1; i <= N; ++i)
    for (int j = i; j <= N; ++j) seq[++C].s = i, seq[C].l = j - i + 1;
  std::sort(seq + 1, seq + C + 1, [](dat i, dat j) {
    int d = lcp[i.s][j.s];
    if (std::min(i.l, j.l) > d) return str[i.s + d] < str[j.s + d];
    return i.l < j.l;
  });
  C = std::unique(
          seq + 1, seq + C + 1,
          [](dat i, dat j) { return i.l == j.l && lcp[i.s][j.s] >= i.l; }) -
      seq - 1;
  int l = 1, r = C, mid, ans = -1;
  while (l <= r) {
    mid = (l + r) >> 1;
    if (Solve(seq[mid]) >= K)
      ans = mid, l = mid + 1;
    else
      r = mid - 1;
  }
  str[seq[ans].s + seq[ans].l] = '\0';
  printf("%s\n", str + seq[ans].s);
  return 0;
}
