#include<iostream>
#include<algorithm>
#define DIM 100005
using namespace std;
int n, m, v, p, i, sol;
int w[DIM];
long long sp[DIM], sum;
int main(){
    cin>> n >> m >> v >> p;
    for(i = 1; i <= n; i++){
        cin>> w[i];
    }
    sort(w + 1, w + n + 1);
    for(i = 1; i <= n; i++){
        sp[i] = sp[i - 1] + w[i];
    }
    for(i = 1; i <= n; i++){
        if(w[i] + m >= w[n - p + 1]){
            sum = (i + p - 1) * 1LL * m;
            if(i < n - p + 1){
                sum += (w[i] + m) * 1LL * (n - p + 1 - i) - (sp[n - p + 1] - sp[i]);
            }
            if(sum >= m * 1LL * v){
                sol++;
            }
        }
    }
    cout<< sol;
}
