import std.stdio, std.conv, std.string, std.array, std.range, std.algorithm, std.container;
import std.math, std.random, std.bigint, std.datetime, std.format;
void main(string[] args){ if(args.length > 1) if(args[1] == "-debug") DEBUG = 1; solve(); }
void log()(){ writeln(""); } void log(T, A ...)(T t, lazy A a){ if(DEBUG) write(t, " "), log(a); } bool DEBUG = 0; 
string rstring(){ static string[] ss; while(!ss.length) ss = readln.chomp.split; string res = ss[0]; ss.popFront; return res; }
T rtype(T)(){ return rstring.to!T; } alias rint = rtype!int, rlong = rtype!long, rreal = rtype!real;
T[] rtypes(T)(int n){ return n.iota.map!(i => rtype!T()).array; } alias rint = rtypes!int, rlong = rtypes!long, rreal = rtypes!real;
T[][] rtypess(T)(int n, int m){ return n.iota.map!(i => rtypes!T(m)).array; } alias rint = rtypess!int, rlong = rtypess!long, rreal = rtypess!real;
T chmin(T)(ref T x, T y){ if(x > y) x = y; return x; } T chmax(T)(ref T x, T y){ if(x < y) x = y; return x; }

// ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- ----- //

void solve(){
	int n = rint;
	long m = rlong, v = rlong, p = rlong;
	log("n:", n, "m:", m, "v:", v, "p:", p);

	long[] as = rlong(n);
	as.sort!"a>b"();
	log("as:", as);

	long b = as[p - 1]; // 第p位のスコア。ボーダーになる
	log("b:", b);

	int ans;
	long sum;
	long u = 0;
	foreach(i, a; as){
		log("i:", i, "a:", a, "sum:", sum, "u:", u);
		if(i < p - 1) ans += 1;
		else{
			if(a + m < b) break;
			long h = a + m;
			long q = (u * h - sum) + m * (p - 1) + m * (n - i);
			log("h:", h, "q:", q);
			if(q >= m * v){
				ans += 1;
				sum += a;
				u += 1;
			}
			else break;
		}
		log("sum:", sum, "u:", u, "ans:", ans);
	}
	ans.writeln;
}