Problem:
Score : 700 points

Problem 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?

Constraints

2 \le N \le 10^5

1 \le M \le 10^9

1 \le V \le N - 1

1 \le P \le N - 1

0 \le A_i \le 10^9

Input

Input is given from Standard Input in the following format:

N M V P
A_1 A_2 ... A_N

Output

Print the number of problems that have a chance to be chosen for the problemset.

Sample Input 1

6 1 2 2
2 1 1 3 0 2

Sample Output 1

5

If the only judge votes for problems 2 and 5, the scores will be 2 2 1 3 1 2.
The problemset will consist of problem 4 and one of problems 1, 2, or 6.

If the only judge votes for problems 3 and 4, the scores will be 2 1 2 4 0 2.
The problemset will consist of problem 4 and one of problems 1, 3, or 6.

Thus, problems 1, 2, 3, 4, and 6 have a chance to be chosen for the problemset. On the contrary, there is no way for problem 5 to be chosen.

Sample Input 2

6 1 5 2
2 1 1 3 0 2

Sample Output 2

3

Only problems 1, 4, and 6 have a chance to be chosen.

Sample Input 3

10 4 8 5
7 2 3 6 1 6 5 4 6 5

Sample Output 3

8

Solution in C++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <bits/stdc++.h>
using namespace std;
#ifndef ONLINE_JUDGE
	#include <boost/multiprecision/cpp_int.hpp>
	#include <boost/multiprecision/cpp_dec_float.hpp>
	using bll = boost::multiprecision::cpp_int;
	using bdouble = boost::multiprecision::cpp_dec_float_100;
#endif
#ifdef LOCAL_DEV
	void debug_impl() { std::cerr << std::endl; }
	template<typename Head, typename... Tail> void debug_impl(Head head, Tail... tail) { std::cerr << " " << head << (sizeof...(tail) ? "," : ""); debug_impl(tail...); }
	#define debug(...) { std::cerr << std::boolalpha << "(" << #__VA_ARGS__ << ") ="; debug_impl(__VA_ARGS__); std::cerr << std::noboolalpha; }
#else
	#define debug(...) {}
#endif
#ifdef LOCAL_TEST
	#define BOOST_STACKTRACE_USE_ADDR2LINE
	#define BOOST_STACKTRACE_ADDR2LINE_LOCATION /usr/local/opt/binutils/bin/addr2line
	#define _GNU_SOURCE
	#include <boost/stacktrace.hpp>
	template<typename T> class dvector : public std::vector<T> {
	public:
		dvector() : std::vector<T>() {}
		explicit dvector(size_t n, const T& value = T()) : std::vector<T>(n, value) {}
		dvector(const std::vector<T>& v) : std::vector<T>(v) {}
		dvector(const std::initializer_list<T> il) : std::vector<T>(il) {}
		dvector(const typename std::vector<T>::iterator first, const typename std::vector<T>::iterator last) : std::vector<T>(first, last) {}
		dvector(const std::string::iterator first, const std::string::iterator last) : std::vector<T>(first, last) {}
		T& operator[](size_t n) {
			try { return this->at(n); } catch (const std::exception& e) {
				std::cerr << boost::stacktrace::stacktrace() << std::endl; return this->at(n);
			}
		}
		const T& operator[](size_t n) const {
			try { return this->at(n); } catch (const std::exception& e) {
				std::cerr << boost::stacktrace::stacktrace() << std::endl; return this->at(n);
			}
		}
	};
	class dbool {
	private:
		bool boolvalue;
	public:
		dbool() : boolvalue(false) {}
		dbool(bool b) : boolvalue(b) {}
		dbool(const dbool &b) : boolvalue(b.boolvalue) {}
		operator bool&() { return boolvalue; }
		operator const bool&() const { return boolvalue; }
	};
	template<typename T> std::ostream& operator<<(std::ostream& s, const dvector<T>& v) {
		for (int i = 0, len = v.size(); i < len; ++i){ s << v[i]; if (i < len - 1) s << "\t"; } return s; }
	template<typename T> std::ostream& operator<<(std::ostream& s, const dvector< dvector<T> >& vv) {
		for (int i = 0, len = vv.size(); i < len; ++i){ s << vv[i] << std::endl; } return s; }
	template<typename T> std::ostream& operator<<(std::ostream& s, const std::set<T>& se) {
		s << "{ "; for (auto itr = se.begin(); itr != se.end(); ++itr){ s << (*itr) << "\t"; } s << "}"; return s; }
	template<typename T> std::ostream& operator<<(std::ostream& s, const std::multiset<T>& se) {
		s << "{ "; for (auto itr = se.begin(); itr != se.end(); ++itr){ s << (*itr) << "\t"; } s << "}"; return s; }
	template<typename T1, typename T2> std::ostream& operator<<(std::ostream& s, const std::map<T1, T2>& m) {
		s << "{" << std::endl; for (auto itr = m.begin(); itr != m.end(); ++itr){ s << "\t" << (*itr).first << " : " << (*itr).second << std::endl; } s << "}"; return s; }
	template<typename T1, typename T2> std::ostream& operator<<(std::ostream& s, const std::pair<T1, T2>& p) { 
		return s << "(" << p.first << ", " << p.second << ")"; }
	#define vector dvector
	#define bool dbool
	class SIGFPE_exception : std::exception {};
	class SIGSEGV_exception : std::exception {};
	void catch_SIGFPE(int e) { std::cerr << boost::stacktrace::stacktrace() << std::endl; throw SIGFPE_exception();	}
	void catch_SIGSEGV(int e) { std::cerr << boost::stacktrace::stacktrace() << std::endl; throw SIGSEGV_exception(); }
	signed convertedmain();
	signed main() { signal(SIGFPE, catch_SIGFPE); signal(SIGSEGV, catch_SIGSEGV); return convertedmain(); }
	#define main() convertedmain()
#endif
//#define int long long
using ll = long long;
//constexpr int INF = 1e9;//INT_MAX=(1<<31)-1=2147483647
constexpr ll INF = (ll)1e18;//(1LL<<63)-1=9223372036854775807
constexpr ll MOD = (ll)1e9 + 7;
constexpr double EPS = 1e-9;
constexpr int dx[4] = {1, 0, -1, 0};
constexpr int dy[4] = {0, 1, 0, -1};
constexpr int dx8[8] = {1, 0, -1, 0, 1, 1, -1, -1};
constexpr int dy8[8] = {0, 1, 0, -1, 1, -1, 1, -1};
#define rep(i, n)   for(ll i=0, i##_length=(n); i< i##_length; ++i)
#define repeq(i, n) for(ll i=1, i##_length=(n); i<=i##_length; ++i)
#define rrep(i, n)   for(ll i=(n)-1; i>=0; --i)
#define rrepeq(i, n) for(ll i=(n)  ; i>=1; --i)
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
#define uniq(v) (v).erase(unique((v).begin(), (v).end()), (v).end())
void p() { std::cout << '\n'; }
template<typename Head, typename... Tail> void p(Head head, Tail... tail) { std::cout << head << (sizeof...(tail) ? " " : ""); p(tail...); }
template<typename T> inline void pv(vector<T> &v) { for(ll i=0, N=v.size(); i<N; i++) std::cout << v[i] << " \n"[i==N-1]; }
template<typename T> inline T gcd(T a, T b) { return b ? gcd(b,a%b) : a; }
template<typename T> inline T lcm(T a, T b) { return a / gcd(a,  b) * b; }
template<typename T> inline bool chmax(T &a, T b) { return a < b && (a = b, true); }
template<typename T> inline bool chmin(T &a, T b) { return a > b && (a = b, true); }

/*-----8<-----template-----8<-----*/

/*-----8<-----library-----8<-----*/

const ll N_MAX = 1e5;
const ll M_MAX = 1e9;
const ll A_I_MAX = 1e9;

ll N, M, V, P;
vector<ll> A;

void solve() {
	scanf("%lld%lld%lld%lld", &N, &M, &V, &P);
	A.assign(N, 0);
	rep(i, N) { scanf("%lld", &A[i]); }

	sort(all(A));
	debug(A);
	//A[0]が採用できる場合のチェックを実装

	auto isOK = [&](ll val) -> bool {
		if(N-P<=val){
			return true;
		}

		ll valpoint=A[val]+M;
		
		if(V-P<=0){
			ll maxpoint=A[N-P];
			debug(val,valpoint,maxpoint);
			if(valpoint>=maxpoint)return true;
			return false;
		}
		/*
		ll umepoint=0;
		ll kijun=A[N-P];
		rep(i,N-P){
			if(i==val)continue;
			umepoint+=kijun-A[i];
		}
		ll maxpoint=A[N-P];
		debug(umepoint,maxpoint,(V-P)*M);
		if(umepoint<(V-P)*M){
			ll amaripoint=(V-P)*M - umepoint;
			ll point=(amaripoint+(N-P)-1)/(N-P);
			maxpoint+=point;
		}
		*/
		
		/*
		ll index1=N-P;
		if(val<index1)index1++;
		ll maxpoint=A[index1]+(V-P)*M/(N-P);
		ll amari=(V-P)*M%(N-P);
		if(amari){
			if(val<amari)amari++;
			chmax(maxpoint,A[amari]+(V-P)*M/(N-P) +1);
		}
		*/
		//debug(val,valpoint,maxpoint);
		/*
		ll maxpoint=A[N-P];

		ll index1=N-P;
		if(val < index1){
			ll kosu=index1-val;
			ll amaripoint=(V-P-val)*M;
			debug(kosu,amaripoint,(V-P-val),M);
			
			ll maxpointtmp=A[index1]+amaripoint/kosu;
			chmax(maxpoint,maxpointtmp);
			ll amari=amaripoint%kosu;
			if(amari){
				chmax(maxpoint,A[val+amari]+amaripoint/kosu +1);
			}
		}
		*/
		ll index1=N-P;
		ll maxpoint=A[N-P];
		if(P+val>=V){
			if(valpoint>=maxpoint)return true;
			return false;
		}

		ll kosu=N-(P-1)-(val+1);
		
		if(kosu<=0){
			return true;
		}
		
		ll amaripoint=(V-P-val)*M;

		debug(kosu,amaripoint);
		//if(val < index1){
			//ll kosu=index1-val;
			//ll amaripoint=(V-P-val)*M;
			//debug(kosu,amaripoint,(V-P-val),M);
			
			ll maxpointtmp=A[index1]+amaripoint/kosu;
			debug(maxpointtmp);
			chmax(maxpoint,maxpointtmp);
			ll amari=amaripoint%kosu;
			if(amari){
				
				maxpointtmp=A[val+amari]+amaripoint/kosu +1;
				debug(maxpointtmp);
				chmax(maxpoint,maxpointtmp);
			}
		//}

		debug(val,valpoint,maxpoint);
		if(valpoint>=maxpoint)return true;
		return false;
	};
	if(isOK(0)){
		p(N);return;
	}

	//ll left = N-1;
	//ll right = 0;//?????
	//while((ll)abs(right - left) > 1) {
	ll right = N-1;
	ll left=0;
	while(right - left > 1) {
		ll mid = left + (right - left) / 2;
		if(!isOK(mid)) left = mid;
		else right = mid;
	}

	
	printf("%lld\n", N-right);
}

// https://atcoder.jp/contests/agc041/tasks/agc041_b
signed main() {
	solve();
	return 0;
}