#include <bits/stdc++.h>
using namespace std;
const int MAXN = 1e3 + 7;
int num[35];
int n, l, k;
char ans[MAXN][MAXN];
int main() {
  cin >> n >> l >> k;
  char ch;
  for (int i = 1; i <= l * n; i++) {
    cin >> ch;
    num[ch - 'a']++;
  }
  int now = 0;
  while (num[now] == 0) now++;
  for (int j = 1; j <= l; j++) {
    for (int i = 1; i <= k; i++) {
      if (ans[i][j - 1] == ans[k][j - 1]) {
        ans[i][j] = 'a' + now;
        num[now]--;
        while (num[now] == 0) now++;
      }
    }
  }
  for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= l; j++) {
      if (ans[i][j]) continue;
      ans[i][j] = 'a' + now;
      num[now]--;
      while (num[now] == 0) now++;
    }
  }
  for (int i = 1; i <= n; i++) {
    cout << ans[i] + 1 << endl;
  }
  return 0;
}
