output_description: Print the number of problems that have a chance to be chosen for the
  problemset.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N M V P
      A_1 A_2 ... A_N
attempt: n, m, v, p = map(int, input().split())
  A = list(map(int, input().split()))
  a = sorted(A, reverse=True)
  key_num = a[p - 1]
  k = a.count(key_num)
  key_idx = a.index(key_num) + k
  c = a[key_idx:]
  C = list(set(c))
  cnt = 0
  for i in c:
      idx = len(C) - C.index(i)
      if key_num <= i + m:
          if v < key_idx + idx:
              cnt += 1
  print(cnt + key_idx)
  
problem_description: Statement
  
  N problems are proposed for an upcoming contest. Problem i has an initial
  integer score of A_i points.
  
  M judges are about to vote for problems they like. Each judge will choose
  exactly V problems, independently from the other judges, and increase the
  score of each chosen problem by 1.
  
  After all M judges cast their vote, the problems will be sorted in non-
  increasing order of score, and the first P problems will be chosen for the
  problemset. Problems with the same score can be ordered arbitrarily, this
  order is decided by the chief judge.
  
  How many problems out of the given N have a chance to be chosen for the
  problemset?
samples: [{"input": "6 1 2 2\n    2 1 1 3 0 2", "output": "5\n    \n\nIf the only judge votes for problems 2 and 5, the scores will be 2 2 1 3 1 2.\nThe problemset will consist of problem 4 and one of problems 1, 2, or 6.\n\nIf the only judge votes for problems 3 and 4, the scores will be 2 1 2 4 0 2.\nThe problemset will consist of problem 4 and one of problems 1, 3, or 6.\n\nThus, problems 1, 2, 3, 4, and 6 have a chance to be chosen for the\nproblemset. On the contrary, there is no way for problem 5 to be chosen.\n\n* * *"}, {"input": "6 1 5 2\n    2 1 1 3 0 2", "output": "3\n    \n\nOnly problems 1, 4, and 6 have a chance to be chosen.\n\n* * *"}, {"input": "10 4 8 5\n    7 2 3 6 1 6 5 4 6 5", "output": "8"}]