#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  long long n, l, k;
  cin >> n >> l >> k;
  vector<long long> v(26, 0);
  for (int i = 0; i < n * l; ++i) {
    char c;
    cin >> c;
    v[c - 'a']++;
  }
  vector<string> res(n, string(l, ' '));
  int p = 0, cur = 0, cnt = k;
  for (int i = 0; i < l; ++i) {
    while (v[p] == 0) ++p;
    if (v[p] >= cnt) {
      for (int j = cur; j < k; ++j) {
        res[j][i] = 'a' + p;
      }
      v[p] -= cnt;
    } else {
      for (int j = cur; j < cur + v[p]; ++j) {
        res[j][i] = 'a' + p;
      }
      cnt -= v[p];
      cur += v[p];
      v[p] = 0;
      --i;
    }
  }
  for (int i = 0; i < n; ++i) {
    for (int j = 0; j < l; ++j) {
      while (v[p] == 0) ++p;
      if (res[i][j] == ' ') {
        res[i][j] = 'a' + p;
        --v[p];
      }
    }
    cout << res[i] << endl;
  }
}
