#include <vector>
#include <iostream>
#include <cmath>
#include <map>
#include <unordered_map>
#include <algorithm>
#include <fstream>
#include <unistd.h>
#include <string.h>
#include <string>
#include <numeric>
#include <queue>
#include <deque>
#include <sstream>
#include <iomanip>
#include <set>
#include <stack>
#include <cassert>
#include <functional>
#include <random>
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<vvl> vvvl;
typedef vector<vvvl> vvvvl;
typedef vector<vi> vvi;
typedef vector<vvi> vvvi;
typedef vector<bool> vb;
typedef vector<vector<bool>> vvb;
typedef vector<vvb> vvvb;
typedef vector<vvvb> vvvvb;
typedef vector<string> vs;
typedef vector<vs> vvs;
typedef vector<vvs> vvvs;
typedef vector<char> vc;
typedef vector<vector<char>> vvc;
typedef vector<double> vd;
typedef vector<vd> vvd;
typedef vector<vvd> vvvd;
typedef unordered_map<ll, ll> uii;
typedef unordered_map<ll, ll> uuii;
typedef unordered_map<ll, ll> uuuii;
typedef long double LD;
typedef vector<LD> vld;
typedef vector<pair<LD, LD>> vpld;
typedef pair<ll, ll> PL;
typedef vector<PL> vpl;
typedef vector<vector<PL>> vvpl;
typedef vector<vvpl> vvvpl;
typedef pair<ll, PL> TL;
typedef vector<TL> vtl;
typedef vector<vtl> vvtl;
typedef long double ld;
typedef vector<ld> vld;
const ll LINF = 1e17;
const double pi = 3.1415926535897932;
const string endstr = "\n";
#define FOR(i, a, b) for(ll i = (a); i < b; i++)
#define RFOR(i, a, b) for(ll i = (a); i > b; i--)
#define rep(i, n) for(ll i = 0; i < n; i++)
#define rrep(i, n) for(ll i = n-1; i > -1; i--)
#define FORMAP(it, m) for(auto it = m.begin(); it != m.end(); it++)
#define ff first
#define ss second
#define pb push_back
#define epb emplace_back
#define ALL(X) (X).begin(),(X).end()

template <typename T> T gcd(T a, T b) {return (a == 0) ? b : gcd(b%a, a);}
template <typename T> T lcm(T a, T b) { return a / gcd(a, b) * b;}

bool p_comp_fs(const PL p1, const PL p2){ return p1.first < p2.first;};
bool p_comp_fg(const PL p1, const PL p2){ return p1.first > p2.first;};
bool p_comp_ss(const PL p1, const PL p2){ return p1.second < p2.second;};
bool p_comp_sg(const PL p1, const PL p2){ return p1.second > p2.second;};
template <typename T>
vector<T> uniquen(vector<T> vec /* copy */){
    sort(ALL(vec)); vec.erase(unique(vec.begin(), vec.end()), vec.end()); return vec;
}

inline ll popcnt(ll x){return __builtin_popcountll((unsigned long long)x);};
template<class T> bool chmax(T &a, T b) { if (a < b) { a = b; return true; } return false; }
template<class T> bool chmin(T &a, T b) { if (a > b) { a = b; return true; } return false; }
//friend bool operator<(const tpl& lhs, const tpl& rhs){
//    return std::tie(lhs.l, lhs.r) < std::tie(rhs.l, rhs.r);
//}

bool bit(ll st, ll b){return ((st>>b)&1) == 1;}

ll N, M, V, P;
vl A;

bool check(ll x){
    if(x <= P-1) return true;
    if(P-1 + (N-x) >= V){
        if(A[P-1] <= A[x] + M){
            return true;
        }
        else{
            return false;
        }
    }
    else{
        ll rem = M*(V - (P-1 + (N-x)));
        FOR(i, P-1, x){
            if(rem <= 0) break;
            if(rem >= A[P-1] - A[i]){
                rem -= A[P-1]-A[i];
            }
            else{
                rem = 0; break;
            }
        }
        
        if(rem == 0){
            if(A[P-1] <= A[x] + M){
                return true;
            }
            else{
                return false;
            }
        }
        else{
            ll add = (rem + (x-P+1 - 1)) / (x-P+1);
            if(A[P-1] + add <= A[x] + M){
                return true;
            }
            else{
                return false;
            }
        }
    }
}

int main(){
#ifdef __DEBUG_LOCAL__
    ifstream file("../../../../../in.txt"); if(file.is_open()) cin.rdbuf(file.rdbuf());
#endif
    ios_base::sync_with_stdio(false); cin.tie(nullptr);
    
    cin >> N >> M >> V >> P;
    A = vl(N); rep(i, N) cin >> A[i];
    sort(ALL(A), greater<ll>());
    
    ll ok = P-1, ng = N;
    while(abs(ok-ng) > 1){
        ll mid = (ok+ng)/2;
        if(check(mid)) ok = mid;
        else ng = mid;
    }
    check(3);
    cout << ok+1 << endstr;
    return 0;
}


Measured memory_bytes: 1024