#include <bits/stdc++.h>
using namespace std;

#define int long long
#define itn int
#define For(i, a, b) for (int i = (a); i <= static_cast<int>(b); i++)
#define Forr(i, a, b) for (int i = (a); i >= static_cast<int>(b); i--)
#define rep(i, n) For(i, 0, n - 1)
#define repall(i, arr) for (auto& i : (arr))
#define all(x) (x).begin(), (x).end()
#define pb push_back
#define dump(x) cerr << #x << " = " << (x) << '\n'
#define dump2(x, y) \
    cerr << #x << " = " << (x) << " " << #y << " = " << (y) << '\n'
#define SZ(x) ((int)(x).size())
#define bit(n) (1LL << (n))
constexpr int MOD = 1e9 + 7;

template <typename T>
using pq = priority_queue<T>;
template <typename T>
using pqr = priority_queue<T, vector<T>, greater<T>>;
const int INF = LLONG_MAX / 2;
using P = pair<int, int>;
using vec = vector<int>;
template <typename T>
using mat = vector<vector<T>>;

// clang-format off
template <typename T1, typename T2>
ostream& operator<<(ostream& stream, const pair<T1, T2>& p) { return stream << p.first << "," << p.second; }
template <typename T>
void print(const vector<T> vec) { rep (i, vec.size() - 1) cout << vec[i] << ' '; cout << vec[vec.size() - 1] << '\n'; }
template <typename Arg>
void print(const Arg arg) { cout << arg << '\n'; }
template <typename Head, typename... Args>
void print(const Head head, const Args... args) { cout << head << " "; print(args...); }
template <typename T, typename U>
void init(vector<T>& v, vector<U>& w) { rep (i, v.size()) cin >> v[i] >> w[i]; }
template <typename T>
void init(vector<T>& v) { rep (i, v.size()) cin >> v[i]; }
template <typename T>
T sum_(vector<T> vec, T init = 0) { return std::accumulate(all(vec), T(init)); }
template<typename T>
bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; } return false; }
template<typename T>
bool chmin(T& a, const T& b) { if (a > b) { a = b; return true; } return false; }
template <typename T>
int index(const T& vec, const typename T::iterator it) { return distance(vec.begin(), it); }
template <typename T = int>
mat<T> mmat(int n, int m=0) { return mat<T>(n, vector<T>(m)); }
template <typename T = int>
vector<T> ivec(int n) { vector<T> v(n); init(v); return v; }
// clang-format on

void yn(bool tf) { print(tf ? "Yes" : "No"); }
void YN(bool tf) { print(tf ? "YES" : "NO"); }

int gcd(int a, int b) { return b ? gcd(b, a % b) : a; }
// -------------------------------------------------------------------
// sort 1 2 3 4
// pqr 1 2 3 must impl >

signed main() {
    cin.tie(0), cout.tie(0), ios::sync_with_stdio(false);
    int n, m, v, p;
    cin >> n >> m >> v >> p;
    vec a = ivec(n);
    sort(all(a), greater<int>());
    rep (i, p - 1)
        a[i] += m;
    // if v < p
    v -= p;

    vec rui(n);
    rui[0] = a[0];
    For(i, 1, n - 1) rui[i] = rui[i - 1] + a[i];

    int low = 0;
    int high = n;
    int mid = -1;
    while (high - low > 1) {
        mid = (high + low) / 2;
        bool ok = false;

        if (mid <= p - 1) {
            ok = true;
        } else if (a[mid] + m < a[p - 1]) {
            ok = false;
        } else {
            int rest = (v - (n - mid - 1)) * m;
            if (rest <= 0) {
                ok = true;
            } else {
                int cap = (a[mid] + m) * (mid - 1 - (p - 2)) -
                          (rui[mid - 1] - rui[p - 2]);
                ok = (cap >= rest);
            }
        }

        if (ok)
            low = mid;
        else
            high = mid;
    }
    print(low + 1);

    return 0;
}


Measured memory_bytes: 1920