#include <algorithm>
#include <bitset>
#include <climits>
#include <cmath>
#include <cstdio>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <unordered_map>
#include <vector>

#define MOD 1000000007
#define MOD2 998244353
#define int long long
//#define PI 3.14159265358979

#define rep(i, n) for (int i = 0; i < (int)(n); i++)

using namespace std;

template < typename T >
ostream &operator<<(ostream &os, const vector< T > &A) {
	for (int i = 0; i < A.size(); i++)
		os << A[i] << " ";
	os << endl;
	return os;
}
template <>
ostream &operator<<(ostream &os, const vector< vector< int > > &A) {
	int N = A.size();
	int M;
	if (N > 0)
		M = A[0].size();
	for (int i = 0; i < N; i++) {
		for (int j = 0; j < M; j++)
			os << A[i][j] << " ";
		os << endl;
	}
	return os;
}

typedef pair< int, int > pii;
typedef long long ll;

struct edge {
	int from, to, d, c;
	edge(int _from = 0, int _to = 0, int _d = 0, int _c = 0) {
		from = _from;
		to = _to;
		d = _d;
		c = _c;
	}
	bool operator<(const edge &rhs) const {
		return (d == rhs.d) ? (c < rhs.c) : (d < rhs.d);
	}
};
struct aabb {
	int x1, y1, x2, y2;
	aabb(int x1, int y1, int x2, int y2) : x1(x1), y1(y1), x2(x2), y2(y2) {}
};

typedef vector< edge > edges;
typedef vector< edges > graph;
struct flow {
	int to, cap, rev, cost;
	flow(int to = 0, int cap = 0, int rev = 0, int cost = 0) : to(to), cap(cap), rev(rev), cost(cost) {}
};
typedef vector< vector< flow > > flows;

const int di[4] = {0, -1, 0, 1};
const int dj[4] = {-1, 0, 1, 0};
const int ci[5] = {0, 0, -1, 0, 1};
const int cj[5] = {0, -1, 0, 1, 0};
const ll LINF = LLONG_MAX / 2;
const int INF = INT_MAX / 2;
const double PI = acos(-1);

int pow2(int n) { return 1 << n; }
template < typename T, typename U >
bool chmin(T &x, const U &y) {
	if (x > y) {
		x = y;
		return true;
	}
	return false;
}
template < typename T, typename U >
bool chmax(T &x, const U &y) {
	if (x < y) {
		x = y;
		return true;
	}
	return false;
}

struct initializer {
	initializer() {
		cout << fixed << setprecision(11);
	}
};
initializer _____;

int N, M, K, T, Q, H, W, V, P;
bool check(vector< int > &A, int m) {
	if (m < P)
		return true;
	vector< int > B = A;

	rep(i, P - 1) {
		B[i] += M;
	}

	int V2 = V - P;
	while (A[m - 1] == A[m])
		--m;
	B[m] += M;
	if (V2 <= 0) {
		sort(B.rbegin(), B.rend());
		return B[P - 1] <= A[m] + M;
	}

	for (int i = m + 1; i < N; i++) {
		B[i] += M;
		V2--;
	}
	int M2 = M;
	if (V2 <= 0) {
		sort(B.rbegin(), B.rend());
		return B[P - 1] <= A[m] + M;
	}
	vector< int > tmp(V2, M);
	int target = B[m];
	int j = 0;
	for (int i = m - 1; i >= P - 1; i--) {
		int k = min(target - B[i], tmp[j]);
		if (k < 0) {
			return false;
		}
		B[i] += k;
		tmp[j] -= k;
		if (tmp[j] == 0)
			++j;
		if (j == V2)
			break;
		if (B[i] < target) {
			k = min(M - k, target - B[i]);
			tmp[j] -= k;
			B[i] += k;
		}
	}
	if (j == V2) {
		sort(B.rbegin(), B.rend());
		return B[P - 1] <= A[m] + M;
	} else
		return false;
}
signed main() {
	cin >> N >> M;
	cin >> V >> P;
	vector< int > A(N);
	rep(i, N) cin >> A[i];
	sort(A.rbegin(), A.rend());
	int ans;
	int l = 0, r = N;
	while (r - l > 1) {
		int m = (l + r) / 2;
		if (check(A, m)) {
			l = m;
		} else {
			r = m;
		}
	}
	cout << l + 1 << endl;
	return 0;
}

Measured memory_bytes: 2276