#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
  ind1 = ind - hm
  ind2 = ind - hm
  c = 1
  bord = a[ind2]
  cup = 0
  @m.times do |i|
    while ind1 >= 0
      if(a[ind1-1] <= a[ind1] + cup/c)
        c += 1
        ind1 -= 1
      else
        break
      end
    end
    while ind2 < ind
      if(a[ind2]+i <= a[ind2-1] + cup/c)
        c += 1
        ind2 += 1
      else
        break
      end
    end
    p hm-(ind-ind2)
    cup += hm-(ind-ind2)
  end
  return (a[ind] + @m >= @b + r_up(cup,c))
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 + [-9999999]
b = a[p-1]
@b = b
@m = m
@n = n
@v = v
@p  = p

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