#!usr/bin/env python3

from collections import defaultdict,deque

from heapq import heappush, heappop

from itertools import permutations

import sys

import math

import bisect

def LI(): return [int(x) for x in sys.stdin.readline().split()]

def I(): return int(sys.stdin.readline())

def LS():return [list(x) for x in sys.stdin.readline().split()]

def S():

    res = list(sys.stdin.readline())

    if res[-1] == "\n":

        return res[:-1]

    return res

def IR(n):

    return [I() for i in range(n)]

def LIR(n):

    return [LI() for i in range(n)]

def SR(n):

    return [S() for i in range(n)]

def LSR(n):

    return [LS() for i in range(n)]



sys.setrecursionlimit(1000000)

mod = 1000000007



def solve():

    n,m,v,p = LI()

    a = LI()

    a.sort()

    l = -1

    r = n-1

    while r-l > 1:

        i = (l+r) >> 1

        ai = a[i]

        aim = ai+m

        ri = bisect.bisect_right(a,aim)

        if n-ri >= p:

            l = i

            continue

        cnt = 0

        for j in range(n-p+1):

            if i == j:

                continue

            cnt += min(m,max(0,aim-a[j]))

        if cnt >= m*(v-p):

            r = i

        else:

            l = i

    print((n-r))

    return



#Solve

if __name__ == "__main__":

    solve()

#!usr/bin/env python3

from collections import defaultdict,deque

from heapq import heappush, heappop

from itertools import permutations

import sys

import math

import bisect

def LI(): return [int(x) for x in sys.stdin.readline().split()]

def I(): return int(sys.stdin.readline())

def LS():return [list(x) for x in sys.stdin.readline().split()]

def S():

    res = list(sys.stdin.readline())

    if res[-1] == "\n":

        return res[:-1]

    return res

def IR(n):

    return [I() for i in range(n)]

def LIR(n):

    return [LI() for i in range(n)]

def SR(n):

    return [S() for i in range(n)]

def LSR(n):

    return [LS() for i in range(n)]



sys.setrecursionlimit(1000000)

mod = 1000000007



def solve():

    n,m,v,p = LI()

    a = LI()

    a.sort()

    l = -1

    r = n-1

    while r-l > 1:

        i = (l+r) >> 1

        ai = a[i]

        aim = ai+m

        ri = bisect.bisect_right(a,aim)

        if n-ri >= p:

            l = i

            continue

        cnt = 0

        for j in range(n-p+1):

            if i == j:

                continue

            cnt += min(m,aim-a[j])

        if cnt >= m*(v-p):

            r = i

        else:

            l = i

    print((n-r))

    return



#Solve

if __name__ == "__main__":

    solve()

#!usr/bin/env python3
from collections import defaultdict, deque
from heapq import heappush, heappop
from itertools import permutations
import sys
import math
import bisect


def LI():
    return [int(x) for x in sys.stdin.readline().split()]


def I():
    return int(sys.stdin.readline())


def LS():
    return [list(x) for x in sys.stdin.readline().split()]


def S():
    res = list(sys.stdin.readline())
    if res[-1] == "\n":
        return res[:-1]
    return res


def IR(n):
    return [I() for i in range(n)]


def LIR(n):
    return [LI() for i in range(n)]


def SR(n):
    return [S() for i in range(n)]


def LSR(n):
    return [LS() for i in range(n)]


sys.setrecursionlimit(1000000)
mod = 1000000007


def solve():
    n, m, v, p = LI()
    a = LI()
    a.sort()
    l = -1
    r = n - 1
    while r - l > 1:
        i = (l + r) >> 1
        ai = a[i]
        aim = ai + m
        ri = bisect.bisect_right(a, aim)
        if n - ri >= p:
            l = i
            continue
        cnt = 0
        for j in range(n - p + 1):
            if i == j:
                continue
            cnt += min(m, max(0, aim - a[j]))
        if cnt >= m * (v - p):
            r = i
        else:
            l = i
    print((n - r))
    return


# Solve
if __name__ == "__main__":
    solve()

#!usr/bin/env python3
from collections import defaultdict, deque
from heapq import heappush, heappop
from itertools import permutations
import sys
import math
import bisect


def LI():
    return [int(x) for x in sys.stdin.readline().split()]


def I():
    return int(sys.stdin.readline())


def LS():
    return [list(x) for x in sys.stdin.readline().split()]


def S():
    res = list(sys.stdin.readline())
    if res[-1] == "\n":
        return res[:-1]
    return res


def IR(n):
    return [I() for i in range(n)]


def LIR(n):
    return [LI() for i in range(n)]


def SR(n):
    return [S() for i in range(n)]


def LSR(n):
    return [LS() for i in range(n)]


sys.setrecursionlimit(1000000)
mod = 1000000007


def solve():
    n, m, v, p = LI()
    a = LI()
    a.sort()
    l = -1
    r = n - 1
    while r - l > 1:
        i = (l + r) >> 1
        ai = a[i]
        aim = ai + m
        ri = bisect.bisect_right(a, aim)
        if n - ri >= p:
            l = i
            continue
        cnt = 0
        for j in range(n - p + 1):
            if i == j:
                continue
            cnt += min(m, aim - a[j])
        if cnt >= m * (v - p):
            r = i
        else:
            l = i
    print((n - r))
    return


# Solve
if __name__ == "__main__":
    solve()

-            cnt += min(m, max(0, aim - a[j])) +            cnt += min(m, aim - a[j])