#include <bits/stdc++.h>
using namespace std;
int main(){
  long long N, K, X, Y;
  cin >> N >> K >> X >> Y;
  vector<int> A(N);
  for (int i = 0; i < N; i++){
    cin >> A[i];
    A[i] -= 1;
    A[i] = (A[i] + K - 1) / K;
  }
  sort(A.begin(), A.end());
  reverse(A.begin(), A.end());
  Y = min(Y, N * X);
  int t = (Y - 1) / X;
  long long ans = Y * A[t];
  for (int i = 0; i < t; i++){
    ans += (A[i] - A[t]) * X;
  }
  cout << ans << endl;
}