#include <bits/stdc++.h>
using namespace std;
 
using ll = long long;
constexpr ll mod = 1e9 + 7;
#define endl '\n'


template <typename A, typename B>
string to_string(pair<A, B> p);
 
template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p);
 
template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p);
 
string to_string(const string& s) {
  return '"' + s + '"';
}
 
string to_string(const char c) {
  return string(1,c);
}

string to_string(const char* s) {
  return to_string((string) s);
}
 
string to_string(bool b) {
  return (b ? "true" : "false");
}
 
string to_string(vector<bool> v) {
  bool first = true;
  string res = "{";
  for (int i = 0; i < static_cast<int>(v.size()); i++) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(v[i]);
  }
  res += "}";
  return res;
}
 
template <size_t N>
string to_string(bitset<N> v) {
  string res = "";
  for (int i = int(N)-1; i >= 0; --i) {
    res += static_cast<char>('0' + v[i]);
  }
  return res;
}
 
template <typename A>
string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto &x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}";
  return res;
}
 
template <typename A, typename B>
string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}
 
template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ")";
}
 
template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " + to_string(get<2>(p)) + ", " + to_string(get<3>(p)) + ")";
}
 
void debug_out() { cerr << endl; }
 
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}
 
#ifdef COMPETITIVE_PROGRAMMING_LOCAL
#define dbg(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define dbg(...) if(0){}
#endif

 
int main() {
  ios::sync_with_stdio(0); cin.tie(0);
 
  ll N,M,V,P;
  cin >> N >> M >> V >> P;
  vector<ll> A(N);
  for (auto& _a : A) cin >> _a;
  sort(A.rbegin(), A.rend());
  vector<ll> PP(N+1);
  for (int i = 0; i < N; ++i) PP[i+1] = PP[i] + A[i];
  vector<bool> good(N);
  int i = 0;
  for (; i < P; ++i) good[i] = true;
  while (i < N) {
    while (i && i < N && A[i] == A[i-1]) good[i++] = true;
    if (i==N) break;
    ll cnt_inside = i - (P-1);
    ll cnt_outside = N - cnt_inside;
    ll inc_each_timestep = V - cnt_outside;
    dbg(inc_each_timestep);

    ll total_inc = M * inc_each_timestep;
    ll future_val = A[i] + M;
    if (A[P-1] > future_val) {
      dbg("b1");
      break;
    }
      
    ll sum_inside = PP[i] - PP[P-1];
    ll sum_remove = cnt_inside * future_val - sum_inside;
    

    dbg(sum_remove, total_inc);

    if (sum_remove >= total_inc) {
      good[i++] = true;
    } else {
      
      dbg("b2");
      break;
    }
  }




  // ll end = min(N, P + N - V);
  // ll attempt = A[P-1];
  // while (i < end && A[i]+M >= attempt) {
  //   good[i++] = true;
  //   while (i < N && A[i] == A[i-1]) good[i++] = true;
  // }
  // while (i < N && A[i] == A[i-1]) good[i++] = true;
  ll ans = accumulate(good.begin(), good.end(), 0LL);
  dbg(good);
  cout << ans << endl;
}


Measured memory_bytes: 4756