// #pragma GCC target("sse,sse2,sse3,ssse3,sse4")
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#include <list>
 
// hloya template v25
  
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#include <bits/stdc++.h>
#include <valarray>
using namespace std;
  
bool dbg = 0;
  
clock_t start_time = clock();
#define current_time fixed<<setprecision(6)<<(ld)(clock()-start_time)/CLOCKS_PER_SEC
  
#define f first
#define s second
#define mp make_pair
#define pb push_back
#define all(x) (x).begin(), (x).end()
  
#define ll long long
#define ld long double
#define pii pair<int,int>
#define umap unordered_map<int, int>
  
#define files1 freopen("input.txt","r",stdin)
#define files2 freopen("output.txt","w",stdout)
#define files files1;files2
#define fast_io ios_base::sync_with_stdio(0);cin.tie(0)
  
// #define endl '\n'
#define ln(i,n) " \n"[(i) == (n) - 1]
  
void bad(string mes = "Impossible"){cout << mes;exit(0);}
void bad(int mes){cout << mes;exit(0);}
  
template<typename T>
string bin(T x, int st = 2){
    string ans = "";
    while (x > 0){
        ans += char('0' + x % st);
        x /= st;
    }
    reverse(ans.begin(), ans.end());
    return ans.empty() ? "0" : ans;
}
  
template<typename T>
void upmax(T& x, T y) {
    x = max(x, y);
}
  
template<typename T>
void upmin(T& x, T y) {
    x = min(x, y);
}
 
// inline int popcount(int x){
//     int count = 0;
//     __asm__ volatile("POPCNT %1, %0;":"=r"(count):"r"(x):);
//     return count;
// }
  
template<typename T>
T input(){
    T ans = 0, m = 1;
    char c = ' ';
  
    while (!((c >= '0' && c <= '9') || c == '-')) {
        c = getchar();
    }
  
    if (c == '-')
        m = -1, c = getchar();
    while (c >= '0' && c <= '9'){
        ans = ans * 10 + (c - '0'), c = getchar();
    }
    return ans * m;
}
  
template<typename T> void read(T& a) { a = input<T>(); }
template<typename T> void read(T& a, T& b) { read(a), read(b); }
template<typename T> void read(T& a, T& b, T& c) { read(a, b), read(c); }
template<typename T> void read(T& a, T& b, T& c, T& d) { read(a, b), read(c, d); }
  
const int inf = 1e9 + 20;
const short short_inf = 3e4 + 20;
const long double eps = 1e-6;
const int maxn = (int)3e5 + 12;//, base = 1e9 + 7;
const ll llinf = 2e18 + 5;
const double PI = acos(-1.0);
 
const int mod = 1e9 + 7;
  
template<typename T>
T binpow(T n, T s)
{
    if (s <= 0)
        return 1LL;
    if (s % 2 == 0){
        T b = binpow(n, s / 2);
        return ( 1LL * b * b ) % mod;
    } else {
        return (1LL* binpow(n, s - 1) * n) % mod;
    }
}

int main() {
	// files1;
	fast_io;

	int n, m, v, p;
	cin >> n >> m >> v >> p;

	vector<int> a(n);
	for (int i = 0; i < n; i++) {
		cin >> a[i];
	}
	sort(all(a));
	reverse(all(a));

	auto ok = [&](ll x) {
		ll sum = 1ll * v * m;
		for (int i = p - 1; i < n; i++) {
			ll up = min(x - a[i], 1ll * m);
			sum = max(0ll, sum - up);
		}
		for (int i = 0; i + 1 < p; i++) {
			sum = max(0ll, sum - m);
		}
		return sum == 0;
	};

	ll l = a[p-1], r = a[p-1]+m;
	while (r - l > 0) {
		ll c = (l + r) / 2;
		if (ok(c)) {
			r = c;
		} else {
			l = c + 1;
		}
	}

	int ans = 0;
	for (int i = 0; i < n; i++) {
		if (a[i] + m >= l) {
			ans++;
		}
	}
	cout << ans;
	return 0;
}

Measured memory_bytes: 640