#include <iostream>
#include <string>
#include <vector>
#include <algorithm>

using namespace std;

using ll = long long;

template <class T>
using grid = vector<vector<T>>;

#define REP(i,n) for(ll i=0;i<(ll)(n);i++)
#define REPD(i,n) for(ll i=n-1;i>=0;i--)
#define FOR(i,a,b) for(ll i=a;i<=(ll)(b);i++)
#define FORD(i,a,b) for(ll i=a;i>=(ll)(b);i--)

#define input(...) __VA_ARGS__; in(__VA_ARGS__)

void print() {
  std::cout << std::endl;
}

template <class Head, class... Tail>
void print(Head&& head, Tail&&... tail) {
  std::cout << head << " ";
  print(std::forward<Tail>(tail)...);
}

void in() { }

template <class Head, class... Tail>
void in(Head&& head, Tail&&... tail) {
  cin >> head;
  in(std::forward<Tail>(tail)...);
}

int main() {
  ll input(n, k, x, y);

  vector<ll> a(n);
  REP(i, n) cin >> a[i];
  REP(i, n) a[i]--;

  sort(a.begin(), a.end());

  ll thresh = y / x;
  ll all;
  if (thresh > n - 1) {
    all = 0;
    thresh = n;
  }
  else all = (a[n - thresh - 1] + k - 1) / k;
  ll ans = all * y;
  REP(i, thresh) {
    ans += (((a[n - thresh + i] - all * k) + k - 1) / k) * x;
  }
  print(ans);
}