#include <bits/stdc++.h>

using namespace std;

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  int N, K, X, Y;
  cin >> N >> K >> X >> Y;
  vector<int64_t> A(N);
  for (auto &&e : A) {
    cin >> e;
    e = (e + K - 2) / K;
  }
  int x = (Y + X - 1) / X;
  sort(A.begin(), A.end());
  if (N - x < 0) {
    int64_t res = 0;
    for (const auto &e : A) {
      res += e * X;
    }
    cout << res << '\n';
  } else {
    int64_t res = A[N - x] * Y;
    for (int i = N - x; i < N; i++) {
      res += (A[i] - A[N - x]) * X;
    }
    cout << res << '\n';
  }
  return 0;
}