#include<iostream>
#include<algorithm>
#include<vector>
#include<string>
#include<set>
#include<queue>
#include<stack>
#include<bitset>
#include<functional>
#include<map>
#include<iomanip>
#include<limits>
#include<unordered_set> 
#include<cmath>
#include <numeric>
#include <array>
using namespace std;
//long long p = 998244353;
long long p = 1000000007;
#define int long long
#define vel vector<long long>
#define vvel vector<vel>
#define rep(i,n) for(int i=0;i<n;i++)
#define sor(v) sort(v.begin(),v.end())
#define mmax(a,b) a=max(a,b)
#define mmin(a,b) a=min(a,b)
#define mkp make_pair
#define pin pair<int,int>
#define qin pair<pin,int>
#define V vector
#define Endl endl
#define veb vector<bool>
#define fcout cout << fixed << setprecision(15)
#define rev(s) reverse(s.begin(),s.end())
#define lower(h,val) lower_bound(h.begin(),h.end(),val)-h.begin()
#define upper(h,val) upper_bound(h.begin(),h.end(),val)-h.begin()
int max_kai = 150000;
vel kai(max_kai, 1);
vel inv_kai;
int rui(int a, int n, int mod) {
    if (n == 0) { return 1 % mod; }
    int x = rui(a, n / 2, mod);
    x *= x; x %= mod;
    if (n % 2 == 1) { x *= a; x %= mod; }
    return x;
}
vel pa;
vel siz;
int root(int x) {
    if (pa[x] == -1) { return x; }
    int ans = root(pa[x]); pa[x] = ans;
    return ans;
}
void marge(int x, int y) {
    x = root(x);
    y = root(y);
    if (x != y) { pa[x] = y; siz[y] += siz[x]; siz[x] = 0; }
}
int gcd(int x, int y) {
    if (x < y) { return gcd(y, x); }
    if (y == 0) { return x; }
    return gcd(y, x % y);
}
long long modinv(long long a, long long m) {
    long long b = m, u = 1, v = 0;
    while (b) {
        long long t = a / b;
        a -= t * b; swap(a, b);
        u -= t * v; swap(u, v);
    }
    u %= m;
    if (u < 0) u += m;
    return u;
}
vel uni(vel x) {
    if (x.size() == 0) { return x; }
    sor(x);
    int n = x.size();
    vel ans(1, x[0]);
    for (int j = 1; j < n; j++) {
        if (x[j - 1] != x[j]) { ans.push_back(x[j]); }
    }
    x = ans;
    return x;
}
void pr(vel& v) {
    int n = v.size();
    if (n != 0) {
        cout << v[0];
        rep(i, n - 1) {
            cout << " " << v[i + 1];
        }
        cout << endl;
    }
}
int sol(int x, int k) {
    if (x == 0 || k == 0) { return 0; }
    return x + sol(x / 2, k - 1);
}
vel pri(int n) {
    veb ans(n, true);
    vel prime;
    for (int j = 2; j < n; j++) {
        if (ans[j]) {
            prime.push_back(j);
            for (int k = 2; j * k < n; k++) {
                ans[j * k] = false;
            }
        }
    }
    return prime;
}
bool solve(vel& a, int se, int k, int m) {
    int n = a.size();
    rep(i, n) {
        if (a[i] < se) { a[i] = se; k = k + a[i] - se; }
    }
    if (k < 0) { return false; }
    int ex1 = 0;
    int ex2 = 0;
    rep(i, n) {
        ex1 += n - se;
        mmax(ex2, a[i] - se);
    }
    return true;
}
void distu(int n, int m, int k, int l, V<string> &S) {
    int H = S.size();
    if (k != 0 || l != 0) {
        n += k;
        m += l;
        bool fl = false;
        while (0<=n&&n<H&&0<=m&&m<H) {
            if (S[n][m] == 'Q'||S[n][m]=='#') { break; }
            if (S[n][m] == 'X') { fl = true; break; }
            n += k;
            m += l;
        }
        if (fl) {
            n -= k; m -= l;
            S[n][m] = '#';
        }
    }
    return;
}
vel bfs(int st, V<V<pin>>& way) {
    int n = way.size();
    vel dist(n, -1); dist[0] = 0;
    queue<int> q;
    q.push(0);
    while (!q.empty()) {
        int x = q.front(); q.pop();
        for (auto nex : way[x]) {
            if (dist[nex.first] >= 0) { dist[nex.first] = dist[x] + 1; }
        }
    }
    return dist;
}
V<V<pin>> dbl(V<pin>& v) {
    int n = v.size();
    V<V<pin>> ans(19, V<pin>(n));
    ans[0] = v;
    rep(i, 18) {
        rep(j, n) { 
            ans[i + 1][j] = mkp(ans[i][ans[i][j].first].first,ans[i][ans[i][j].first].second+ans[i][j].second); 
        }
    }
    return ans;
}
bool solve(vel a, int n, int m, int v, int p,int che) {
    a[che] += m;
    if (che < p) { return true; }
    v -= p;
    if (a[che] < a[p-1]) { return false; }
    if (v <= 0) { return true; }
    int sum = m * v;
    for (int i = p - 1; i < n; i++) {
        if (i != che) {
            sum -= min(m, a[che] - a[i]);
        }
    }
    return (sum<=0);
}
signed main(){
    int n, m, v, p; cin >> n >> m >> v >> p;
    vel a(n);
    rep(i, n) { cin >> a[i]; }
    sor(a); rev(a);
    int ok = 0; int ng = n;
    while (ng - ok > 1) {
        int mid = (ok + ng) / 2;
        if (solve(a, n, m, v, p,mid)) { ok = mid; }
        else { ng = mid; }
    }
    cout << ng << endl;
    return 0;
}

Measured memory_bytes: 3072