import std.stdio, std.string, std.conv, std.algorithm;
void main(){
	long n, m, v, p, i, u, a;
	scanf("%d %d %d %d\n", &n, &m, &v, &p);
	auto A = readln.split.to!(long[]);
	A.sort!"a>b"();

	long sum;
	for(i = p - 1; i < A.length; i ++){
		a = A[i];
		if(a + m >= A[p - 1] && (i - (p - 1)) * (a + m) - sum + m * (p - 1 + n - i) >= m * v) sum += a;
		else break;
	}
	i.writeln;
}