import java.io.*
import java.util.*
import java.lang.*
import java.lang.Math.*

fun bsCondOpCl(A: LongArray, L: Int, R: Int, M: Long, V: Long, P: Long): Int {
    val N = A.size

    fun isCondition(A: LongArray, m: Int): Boolean {
        var sum = M*V
        val before = BooleanArray(N){false}
        val AmMax = A[m] + M
        before[m] = true
        var cnt = 1L
        for (i in 0 until N) {
            if (before[i]) continue
            if (cnt >= P) break
            else {
                before[i] = true
                cnt++
            }
        }

        for (i in 0 until N) {
            if (before[i]) {
                sum -= M
            } else {
                if (AmMax < A[i]) return false
                sum -= min(AmMax - A[i], M)
            }
        }

        return sum <= 0L
    }

    var l = L; var r = R
    while (l+1 < r) {
        val m = (l + r) / 2
        if (isCondition(A, m)) {
            //r = m
            l = m
        } else {
            //l = m
            r = m
        }
    }
    return r
}

fun solve() {
    val (N,M,V,P) = rd.readListLong()
    val A = rd.readListLong().sortedDescending()

    val ans = bsCondOpCl(A.toLongArray(), 0, N.toInt(), M, V, P)
    println(ans)
}


//val rd = debug.Reader("agc", "041", "b", "sample-3")
val rd = Reader()


fun main(args: Array<String>) {
    try {
        var exception: Throwable? = null
        val sth = Thread(null, SolveThread(), "solveThread", 128 * 1024 * 1024)
        sth.setUncaughtExceptionHandler { _, e -> exception = e }
        sth.start(); sth.join()
        if (exception != null) throw exception!! }
    catch (e: Exception) { throw e }
    finally { rd.close() }
}
const val MOD = 1_000_000_007L; const val INF = Int.MAX_VALUE/2; const val LINF = Long.MAX_VALUE/2
const val EPS = 1e-9; fun DBLEQ(a: Double, b: Double): Boolean {return abs(a - b) < EPS}
data class IntPair(val first: Int, val second: Int); data class LongPair(val first: Long, val second: Long)
data class To(val idx: Int, val cost: Long)
typealias ALI = ArrayList<Int>
fun <T>edge(V: Int): Array<ArrayList<T>> { return Array(V){ArrayList<T>()} }
val errPrintln: (Any) -> Unit = { msg -> System.err.println(msg) }
fun rAssert(exp: Boolean, lazyMsg: () -> String = {""}) {
    if (!exp) { val msg = lazyMsg(); errPrintln("EAssert Error: $msg"); throw Error(msg) }
}
fun tAssert(exp: Boolean, lazyMsg: () -> String = {""}) {
    if (!exp) { val msg = lazyMsg(); errPrintln("TAssert Error: $msg"); Thread.sleep(3000) }
}
class SolveThread : Runnable {
    override fun run() { solve() }
}
class Reader {
    private val br = BufferedReader(InputStreamReader(System.`in`))
    val readString: () -> String = { br.readLine() }
    val readInt: () -> Int = { br.readLine().toInt() }
    val readLong: () -> Long = { br.readLine().toLong() }
    val readDouble: () -> Double = { br.readLine().toDouble() }
    val readListInt: () -> List<Int> = { br.readLine().split(' ').map { it.toInt() } }
    val readListLong: () -> List<Long> = { br.readLine().split(' ').map { it.toLong() } }
    val readIntArray: () -> IntArray = { readListInt().toIntArray() }
    val readLongArray: () -> LongArray = { readListLong().toLongArray() }
    val readListStringCol: (Int) -> List<String> = { N -> (0 until N).map { readString() } }
    val readListIntCol: (Int) -> List<Int> = { N -> (0 until N).map { readInt() } }
    val readListIntCols: (Int) -> List<List<Int>> = { N -> (0 until N).map { readListInt() } }
    val readListLongCol: (Int) -> List<Long> = { N -> (0 until N).map { readLong() } }
    val readListLongCols: (Int) -> List<List<Long>> = { N -> (0 until N).map { readListLong() } }
    val close: () -> Unit = { br.close() }
    protected fun finalize() { close() }
}


Measured memory_bytes: 60308