#exec({'RUBY_THREAD_VM_STACK_SIZE'=>'100000000'},'/usr/bin/ruby', $0) if !ENV['RUBY_THREAD_VM_STACK_SIZE']

def inpf() a=gets.chomp.split(" ").map(&:to_f)end

def inps() a=gets.chomp.split(" ")end

def copy(a) Marshal.load(Marshal.dump(a)) end

def kaijo(n,r = 10**9+7)(n < 2)? 1 : (2..n).inject{|memo,u|memo=(memo*u)%r} end

def na(n,d=0) Array.new(n,d)end

def na2(n,m,d=0) Array.new(n){Array.new(m,d)}end

def na3(n,m,l,d=0) Array.new(n){Array.new(m){Array.new(l,d)}}end

def inp() a=gets.chomp.split(" ").map(&:to_i)end

def r_up(a, b) (a+b-1)/b end

def sum(a) a.inject(:+) end

def big(a,b) return (a>b)? a:b end

def small(a,b) return (a<b)? a:b end

def j(a,ind)
  hm = [0,@v-@p+1-(@n-ind)].max
  sp = ind - @p +1
  am = sp - hm
  spc = am*@m
  f = true
  buf = a[ind] + @m
  a[(@p-1)...ind].each do |d|
    if(d > buf)
      return false
    end
    spc -= d-a[ind]
    if(spc < 0)
      return false
    end
  end
  return f
end

def b_ser(a,l,r)
  mid = (l + r)/2
  if(l==r-1)
    return l
  elsif(j(a,mid))
    return b_ser(a,mid, r)
  else  #j(mid) == false
    return b_ser(a,l, mid)
  end
end

n,m,v,p = inp
a = inp.sort.reverse + [-1e20]
b = a[p-1]
@b = b
@m = m
@n = n
@v = v
@p  = p

p b_ser(a,0,n+1)+1