using System;
using System.Collections.Generic;
using System.Linq;
using System.IO;
using System.Text;
using static System.Math;
using static System.Array;
using static AtCoder.Tool;
namespace AtCoder
{
    class AC
    {
        const int MOD = 1000000007;
        const int INF = int.MaxValue / 2;
        const long SINF = long.MaxValue / 2;
        const double EPS = 1e-8;
        static readonly int[] dx = { 0, 1, 0, -1 };
        static readonly int[] dy = { 1, 0, -1, 0 };
        static List<List<int>> G = new List<List<int>>();
        //static List<List<Edge>>G = new List<List<Edge>>();
        //static List<Edge> E = new List<Edge>();

        static void Main(string[] args)
        {
            //var sw = new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
            //Console.SetOut(sw);
            var cin = new Scanner();

            var input = cin.ReadSplit();
            int N = input[0];
            long M = input[1];
            int V = input[2];
            int P = input[3];
            var A = cin.ReadSplitL();
            Sort(A);
            Reverse(A);
            int ans = 0;
            long ressum = 0;
            //Console.WriteLine(string.Join(",", A));
            for(long i = 0; i < N; i++)
            {
                //Console.WriteLine($"{i}:{A[i]}");
                if (i < P)//元々上位
                {
                    ans++;continue;
                }
                
                long cur = A[i] + M;
                ressum += A[i - 1];
                if (cur < A[P - 1]) { break; }
                if (A[i] == A[i - 1]) { ans++;continue; }
                long res = V - (N - i);//下位には投票しておく
                //Console.WriteLine($"res={res}");
                if (res <= P - 1)
                {
                    ans++;
                    continue;
                }
                res -= P - 1;

                /*Console.WriteLine(ressum);
                Console.WriteLine((i - P + 1) * cur - ressum);
                Console.WriteLine(res);*/
                if ((i - P + 1) * (A[i] + M) - ressum >= res * M) { ans++; }
                else { break; }
            }
            Console.WriteLine(ans);

            
            //Console.Out.Flush();
        }
        
        struct Edge
        {
            public int from;

            public int to;
            public long dist;
            public Edge(int t, long c)
            {
                from = -1;
                to = t;
                dist = c;
            }
            public Edge(int f, int t, long c)
            {
                from = f;
                to = t;
                dist = c;
            }

        }
    }
    public class Scanner
    {
        public int[] ReadSplit()
        {
            return ConvertAll(Console.ReadLine().Split(), int.Parse);
        }
        public long[] ReadSplitL()
        {
            return ConvertAll(Console.ReadLine().Split(), long.Parse);
        }
        public double[] ReadSplitD()
        {
            return ConvertAll(Console.ReadLine().Split(), double.Parse);
        }
    }
    public static class Tool
    {
        static public void Initialize<T>(ref T[] array, T initialvalue)
        {
            for (var i = 0; i < array.Length; i++)
            {
                array[i] = initialvalue;
            }
        }
        static public void Swap<T>(ref T a, ref T b)
        {
            T keep = a;
            a = b;
            b = keep;
        }

        static public void Display<T>(T[,] array2d, int n, int m)
        {
            for (var i = 0; i < n; i++)
            {
                for (var j = 0; j < m; j++)
                {
                    Console.Write($"{array2d[i, j]} ");
                }
                Console.WriteLine();
            }
        }

        static public long LPow(int a, int b)
        {
            return (long)Pow(a, b);
        }
    }
}


Measured memory_bytes: 21088