#include<algorithm>
#include<cstdio>
using namespace std;

const int MAX_N = 1e5;
int n, m, v, p;
int a[MAX_N];

int main() {
    scanf("%d %d %d %d", &n, &m, &v, &p);
    for (int i = 0; i < n; i++) scanf("%d", &a[i]);
    sort(a, a + n);
    long sum = static_cast<long>(m) * (v - n + 1), diff = 0;
    int ans = p;
    for (int i = n - p - 1; i >= 0; i--) {
        if (a[i] + m >= a[n - p]) {
            if (diff + static_cast<long>(a[i] + m - a[n - p])
                     * (n - p - i) >= sum) ans++;
        }
        else break;
        diff += a[n - p] - a[i];
        sum += m;
    }
    printf("%d\n", ans);
    return 0;
}
