#pragma region template
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;
using ld = long double;
using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using vll = vector<ll>;
using vvll = vector<vll>;
using vvvll = vector<vvll>;
using vld = vector<ld>;
using vvld = vector<vld>;
using vvvld = vector<vvld>;
using vs = vector<string>;
using pll = pair<ll, ll>;
using vp = vector<pll>;
template <typename T>
using pqrev = priority_queue<T, vector<T>, greater<T>>;
#define rep(i, n) for (ll i = 0, i##_end = (n); i < i##_end; i++)
#define repb(i, n) for (ll i = (n)-1; i >= 0; i--)
#define repr(i, a, b) for (ll i = (a), i##_end = (b); i < i##_end; i++)
#define reprb(i, a, b) for (ll i = (b)-1, i##_end = (a); i >= i##_end; i--)
#define ALL(a) (a).begin(), (a).end()
#define SZ(x) ((ll)(x).size())
//
const ll MOD = 1e9 + 7;
/*/
const ll MOD = 998244353;
//*/
const ll INF = 1e+18;
const ld EPS = 1e-12L;
const ld PI = acos(-1.L);
inline ll GCD(ll a, ll b) { return b ? GCD(b, a % b) : a; }
inline ll LCM(ll a, ll b) { return a / GCD(a, b) * b; }
template <typename S, typename T>
inline bool chmax(S &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <typename S, typename T>
inline bool chmin(S &a, const T &b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}
#ifdef OJ_LOCAL
#include "dump.hpp"
#else
#define dump(...) ((void)0)
#endif
template <typename T>
bool print_(const T &a) {
  cout << a;
  return true;
}
template <typename T>
bool print_(const vector<T> &vec) {
  for (auto &a : vec) {
    cout << a;
    if (&a != &vec.back()) {
      cout << " ";
    }
  }
  return false;
}
template <typename T>
bool print_(const vector<vector<T>> &vv) {
  for (auto &v : vv) {
    for (auto &a : v) {
      cout << a;
      if (&a != &v.back()) {
        cout << " ";
      }
    }
    if (&v != &vv.back()) {
      cout << "\n";
    }
  }
  return false;
}
void print() { cout << "\n"; }
template <typename Head, typename... Tail>
void print(Head &&head, Tail &&... tail) {
  bool f = print_(head);
  if (sizeof...(tail) != 0) {
    cout << (f ? " " : "\n");
  }
  print(forward<Tail>(tail)...);
}
#pragma endregion

ll n, m, v, p;
vll a;

// maximum x (C(x) == true)
bool C(ll mid) {
  if(a[mid]+m < a[p-1]){
    return false;
  }
  vll b;
  {
    ll cnt = 0;
    repb(i, n){
      if(i != mid){
        b.emplace_back(a[i]);
        cnt++;
      }
      if(cnt == n-p) break;
    }
  }
  rep(i, SZ(b)){
    b[i] = a[mid]+m-b[i];
  }
  map<ll, ll> mp;
  rep(i, SZ(b)){
    mp[b[i]]++;
  }
  ll f = 0;
  for(auto&& e: mp){
    f += min(e.first, m) * e.second;
  }
  f /= m;
  return f >= v-p;
}

ll BinarySearchMax(ll lb, ll ub) {
  // 返り値の範囲：[lb, ub)
  // 条件：
  //   (lb, ub)で検証できること
  //   C(lb)==true, C(ub)==false
  while (ub - lb > 1) {
    ll mid = lb + ((ub - lb) >> 1);
    if (C(mid)) {
      // [mid, ub)
      lb = mid;
    } else {
      // [lb, mid)
      ub = mid;
    }
  }
  return lb;
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(15);
  cin >> n >> m >> v >> p;
  rep(i, n){
    ll b;
    cin >> b;
    a.emplace_back(b);
  }
  sort(ALL(a));
  reverse(ALL(a));
  print(BinarySearchMax(0, n)+1);
}


Measured memory_bytes: 8088