import std.algorithm;
import std.array;
import std.ascii;
import std.bigint;
import std.complex;
import std.container;
import std.conv;
import std.functional;
import std.math;
import std.range;
import std.stdio;
import std.string;
import std.typecons;

auto readInts() {
	return array(map!(to!int)(readln().strip().split()));
}
auto readInt() {
	return readInts()[0];
}
auto readLongs() {
	return array(map!(to!long)(readln().strip().split()));
}
auto readLong() {
	return readLongs()[0];
}

void readlnTo(T...)(ref T t) {
    auto s = readln().split();
    assert(s.length == t.length);
    foreach(ref ti; t) {
        ti = s[0].to!(typeof(ti));
        s = s[1..$];
    }
}

bool test(long[] a, long l, long u, long k, long q) {
  return a.split!(x => x < l)
          .filter!(x => x.length >= k)
          .map!(x => min(x.count!(y => y <= u), x.length - k + 1))
          .sum >= q;
}

void main(){
  long n, k, q;
  readlnTo(n, k, q);
  auto a = readLongs();
  long ans = long.max / 2;
  foreach(i; iota(n)) {
    long l = a[i]-1;
    long u = 3_000_000_000;
    while(l + 1 < u) {
      auto m = (l+u)/2;
      if(test(a, a[i], m, k, q)) {
        u = m;
      } else {
        l = m;
      }
    }
    ans = min(ans, u-a[i]);
  }
  writeln(ans);
}

