#include <bits/stdc++.h>
#define fi first
#define se second
#define rep(i,n) for (ll i = 0; i < (n); ++i)
#define rrep(i,n) for (ll i = (n)-1; i >=0; --i)
#define ALL(a) a.begin(),a.end()
#define pb push_back
#define dame { puts("-1"); return 0;}
#define show(x) cerr<<#x<<" = "<<x<<endl;

using namespace std;
using ll = long long;
using ld = long double;
using pi = pair<ll, ll>;

typedef vector<ll> vl;
typedef vector<pi> vp;
template<class T> bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T> bool chmin(T &a, const T &b) { if (a>b) { a=b; return 1; } return 0; }


// auto mod int
// https://youtu.be/L8grWxBlIZ4?t=9858
// https://youtu.be/ERZuLAxZffQ?t=4807 : optimize
// https://youtu.be/8uowVvQ_-Mo?t=1329 : division
const ll mod = 1000000007;
struct mint {
  ll x; // typedef long long ll;
  mint(ll x=0):x((x%mod+mod)%mod){}
  mint operator-() const { return mint(-x);}
  mint& operator+=(const mint a) {
    if ((x += a.x) >= mod) x -= mod;
    return *this;
  }
  mint& operator-=(const mint a) {
    if ((x += mod-a.x) >= mod) x -= mod;
    return *this;
  }
  mint& operator*=(const mint a) { (x *= a.x) %= mod; return *this;}
  mint operator+(const mint a) const { return mint(*this) += a;}
  mint operator-(const mint a) const { return mint(*this) -= a;}
  mint operator*(const mint a) const { return mint(*this) *= a;}
  mint pow(ll t) const {
    if (!t) return 1;
    mint a = pow(t>>1);
    a *= a;
    if (t&1) a *= *this;
    return a;
  }

  // for prime mod
  mint inv() const { return pow(mod-2);}
  mint& operator/=(const mint a) { return *this *= a.inv();}
  mint operator/(const mint a) const { return mint(*this) /= a;}
};
istream& operator>>(istream& is, const mint& a) { return is >> a.x;}
ostream& operator<<(ostream& os, const mint& a) { return os << a.x;}
// combination mod prime
// https://www.youtube.com/watch?v=8uowVvQ_-Mo&feature=youtu.be&t=1619
struct combination {
  vector<mint> fact, ifact;
  combination(int n):fact(n+1),ifact(n+1) {
    assert(n < mod);
    fact[0] = 1;
    for (int i = 1; i <= n; ++i) fact[i] = fact[i-1]*i;
    ifact[n] = fact[n].inv();
    for (int i = n; i >= 1; --i) ifact[i-1] = ifact[i]*i;
  }
  mint operator()(int n, int k) {
    if (k < 0 || k > n) return 0;
    return fact[n]*ifact[k]*ifact[n-k];
  }
} c(200005);



int main() {
  ll n,m,v,p;
  cin >> n>>m>>v>>p;
  
  vl a(n);
  vl c(n+1);
  vector<bool> vv(n, false);

  rep(i, n) cin >> a[i];
  sort(ALL(a));
  reverse(ALL(a));

  ll kijun = a[p-1];

  c[0] = 0;
  rep(i, n) {
    if((kijun - a[i])<0) c[i+1] = c[i] + m;
    else{
      c[i+1] = kijun - a[i] + c[i];
    }
  }

  ll l = 0;
  ll r = n;

  show(c[p+2]);
  
  while(l+1<r){
    show(l);
    show(r);
    ll mid = (l+r)/2;
    if(mid<p-1){
      l = mid;
    }
    else if(a[mid]+m < kijun){
      r = mid;
    }
    else{
      show(c[mid]);
      show((m+a[mid]-kijun));
      show((mid+1-p));
      show(m * (n-mid));
      show(mid);
      ll margin = c[mid] + (m+a[mid]-kijun)*(mid+1-p) + m * (n-mid);
      show(margin);
      cerr << mid << endl;
      if(margin>=m*v) l = mid;
      else r = mid;
    }
  }
  
  cout << l+1 << endl;
  return 0;
}


Measured memory_bytes: 4992