#include <bits/stdc++.h>
using namespace std;
const long long N = 1110;
const long long inf = 1000000007998244353ll;
struct S {
  long long l, r;
} a[N * N];
long long si[N][N];
long long tot;
long long n, m, k;
string s;
long long lcp[N][N];
long long dp[N][N];
long long suffix_sum[N];
long long ri[N];
inline long long add(long long a, long long b) {
  return a + b > inf ? inf : a + b;
}
long long cnt(long long S) {
  for (long long i = 0; i < n; i++) {
    ri[i] = i;
    while (ri[i] != n && si[i][ri[i]] <= S) {
      ri[i]++;
    }
  }
  for (long long i = 0; i < n; i++) {
    dp[i][1] = si[i][n - 1] > si[a[S].l][a[S].r] ? 1 : 0;
  }
  for (long long j = 2; j <= m; j++) {
    suffix_sum[n - 1] = dp[n - 1][j - 1];
    for (long long i = n - 2; i >= 0; i--) {
      suffix_sum[i] = add(dp[i][j - 1], suffix_sum[i + 1]);
    }
    for (long long i = 0; i < n; i++) {
      dp[i][j] = ri[i] == n ? 0 : suffix_sum[ri[i] + 1];
    }
  }
  return dp[0][m];
}
bool cmp(S i, S j) {
  long long p = i.l + lcp[i.l][j.l], q = j.l + lcp[i.l][j.l];
  if (p > i.r || q > j.r) {
    return i.r - i.l < j.r - j.l;
  }
  return s[p] < s[q];
}
signed main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  tot = 0;
  cin >> n >> m >> k >> s;
  for (long long i = 0; i < n; i++) {
    for (long long j = i; j < n; j++) {
      a[tot].l = i;
      a[tot].r = j;
      tot++;
    }
  }
  for (long long i = n - 1; i >= 0; i--) {
    for (long long j = n - 1; j >= 0; j--) {
      lcp[i][j] = s[i] == s[j] ? lcp[i + 1][j + 1] + 1 : 0;
    }
  }
  sort(a, a + tot, cmp);
  for (long long i = 0; i < tot; i++) {
    si[a[i].l][a[i].r] = i;
  }
  long long l = 0, r = tot - 1;
  while (l < r) {
    long long midd = (r + l) / 2;
    if (cnt(midd) >= k) {
      l = midd + 1;
    } else {
      r = midd;
    }
  }
  for (long long i = a[r].l; i <= a[r].r; i++) {
    cout << s[i];
  }
  return 0;
}
