#include<bits/stdc++.h>
#define Tp template<typename Ty>
#define Ts template<typename Ty,typename... Ar>
#define Reg register
#define RI Reg int
#define Con const
#define CI Con int&
#define I inline
#define W while
#define N 100000
#define LL long long
using namespace std;
int n,m,v,p,a[N+5];LL s[N+5];
I bool cmp(CI x,CI y) {return x>y;}//从大到小排序
int main()
{
	RI i;for(scanf("%d%d%d%d",&n,&m,&v,&p),i=1;i<=n;++i) scanf("%d",a+i);
	for(sort(a+1,a+n+1,cmp),i=1;i<=n;++i) s[i]=s[i-1]+a[i];//排序后求前缀和
	for(i=n;i>p;--i) if(a[i]+m>=a[p])//枚举答案，首先要使得加上m后大于等于第p个数
		if(1LL*max(v-p-(n-i),0)*m<=1LL*(a[i]+m)*(i-p)-(s[i-1]-s[p-1])) break;//用1去填平中间的坑
	return printf("%d",i),0;//输出答案（若始终没break则最后i恰好等于p）
}
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using uint = unsigned int;
#define rep(i,n) for(int i=0;i<int(n);i++)
#define rep1(i,n) for(int i=1;i<=int(n);i++)
#define per(i,n) for(int i=int(n)-1;i>=0;i--)
#define per1(i,n) for(int i=int(n);i>0;i--)
#define all(c) c.begin(),c.end()
#define si(x) int(x.size())
#define pb emplace_back
#define fs first
#define sc second
template<class T> using V = vector<T>;
template<class T> using VV = vector<vector<T>>;
template<class T,class U> void chmax(T& x, U y){if(x<y) x=y;}
template<class T,class U> void chmin(T& x, U y){if(y<x) x=y;}
template<class T> void mkuni(V<T>& v){sort(all(v));v.erase(unique(all(v)),v.end());}
template<class S,class T> ostream& operator<<(ostream& o,const pair<S,T> &p){
	return o<<"("<<p.fs<<","<<p.sc<<")";
}
template<class T> ostream& operator<<(ostream& o,const vector<T> &vc){
	o<<"{";
	for(const T& v:vc) o<<v<<",";
	o<<"}";
	return o;
}
constexpr ll TEN(int n) { return (n == 0) ? 1 : 10 * TEN(n-1); }

#ifdef LOCAL
#define show(x) cerr << "LINE" << __LINE__ << " : " << #x << " = " << (x) << endl
void dmpr(ostream& os){os<<endl;}
template<class T,class... Args>
void dmpr(ostream&os,const T&t,const Args&... args){
	os<<t<<" ~ ";
	dmpr(os,args...);
}
#define shows(...) cerr << "LINE" << __LINE__ << " : ";dmpr(cerr,##__VA_ARGS__)
#define dump(x) cerr << "LINE" << __LINE__ << " : " << #x << " = {";  \
	for(auto v: x) cerr << v << ","; cerr << "}" << endl;
#else
#define show(x) void(0)
#define dump(x) void(0)
#define shows(...) void(0)
#endif

int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);		//DON'T USE scanf/printf/puts !!
	cout << fixed << setprecision(20);

	ll N,M,K,P; cin >> N >> M >> K >> P;
	V<ll> A(N); rep(i,N) cin >> A[i];
	sort(all(A),greater<ll>());

	auto can = [&](int i){
		if(i<P) return true;
		ll t = A[i]+M;
		ll f = 0;
		for(int j=P-1;j<N;j++) if(j != i){
			if(t < A[j]) return false;
			f += min(t-A[j],M);
		}
		return f >= M*(K-P);
	};
	int lb = -1, ub = N;
	while(ub-lb>1){
		int m = (lb+ub)/2;
		if(can(m)) lb = m;
		else ub = m;
	}
	cout << lb+1 << endl;
}
