#include <algorithm>
#include <iostream>
#include <vector>
int Nc, Rgc, Cpc;
int arr[100000] = {0};

int checkCount(int kNum) {
  int start = 0;
  int end = 0;
  int count = 0;
  while (end + 1 < Nc) {
    if (arr[end + 1] - arr[start] <= kNum) {
      ++end;
    } else {
      ++start;
    }
    if (end - start + 1 == Cpc) {
      ++count;
      start = end + 1;
      end = start;
    }
  }
  return count;
}

int main() {
  std::cin >> Nc >> Rgc >> Cpc;

  for (int i = 0; i < Nc; ++i) {
    std::cin >> arr[i];
  }
  std::sort(arr, arr + Nc);

  int lhs = -1;
  int rhs = arr[Nc - 1] - arr[0];
  int mid = 0;
  int min = rhs;
  while (lhs < rhs) {
    mid = (lhs + rhs) / 2;
    if (checkCount(mid) < Rgc) {
      lhs = mid + 1;
    } else {
      rhs = mid;
    }
  }
  std::cout << rhs << "\n";
}