#include <bits/stdc++.h>

using namespace std;

int main() {
  ios::sync_with_stdio(0);
  cin.tie(0), cout.tie(0);

  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(a.begin(), a.end());
  int l = -1, r = n - p;
  while (l + 1 < r) {
    int mid = l + r >> 1;
    long long tot = 1ll * (v - mid - p) * m;
    if (a[mid] + m < a[n - p]) {
      l = mid;
      continue;
    }
    for (int i = n - p; i >= mid + 1; --i) {
      tot -= a[mid] + m - a[i];
    }
    if (tot > 0) {
      l = mid;
    } else {
      r = mid;
    }
  }
  cout << n - r;

  return 0;
}
