N,M,V,P,*a = $<.read.split.map &:to_i
Y = a.sort![-P]
X = Y-M
A = a.inject(Hash.new 0) {|h,i| h[i]+=1; h}.to_a
x,y = [X,Y].map {|n| A.bsearch_index {|a| a[0]>=n} }
c = A[0...x].inject(0) {|s,a| s+a[1]}
v = V-P+1-c
A[y][1] = N-P-y+1
x.upto(y) {|i|
  j,k = A[i]
  w = M*v
  t = j+M
  break  if A[i..y].any? {|a| 0 >= (w -= (t-a[0])*a[1])}
  v -= k
  c += k
}
p N-c