package chelper;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import io.InputReader;
import io.OutputWriter;
import misc.SimpleSavingChelperSolution;


public class QUEUE2 extends SimpleSavingChelperSolution {

  public void solve(int testNumber, InputReader in, OutputWriter out) {
    wrapSolve(testNumber, in, out);
  }

  @Override
  public void solve(int testNumber) {
    long n = in.nextLong();
    long m = in.nextLong() + 1;
    long k = in.nextLong();
    long l = in.nextLong();

    long lastFree = 0;

    List<Long> a = new ArrayList<>();
    for (long i = 0; i < n; i++) {
      a.add(in.nextLong());
    }
    Collections.sort(a);
    a.add(k);

    long minWaitTime = m * l;

    for (long i : a) {
      long newlyFree = (i - lastFree) / l;
      lastFree += newlyFree * l;
      m = Math.max(0, m - newlyFree);

      if (m == 0) {
        lastFree = i;
      }

      minWaitTime = Math.min(minWaitTime, Math.max(lastFree + m * l - i, 0));

      m++;
    }

    out.println(minWaitTime);
  }
}