#include <bits/stdc++.h>
using namespace std;

#define ll long long
#define rep(i, n) for (int i = 0; i < (n); i++)
#define P pair<int, int>

int main() {
  int n;
  int k, x, y;
  cin >> n >> k >> x >> y;

  vector<ll> cnt(n);
  rep(i,n) {
    ll a;
    cin >> a;
    a--;
    cnt[i] = (a+k-1)/k;
  }
  sort(cnt.begin(), cnt.end());
  int num = max(-1, n-1-(y/x));
  ll sum_cnt = 0;
  if (num >= 0) sum_cnt = cnt[num];
  ll ans = sum_cnt*y;
  for (int i = num+1; i < n; i++) {
    ans += (cnt[i]-sum_cnt)*x;
  }
  cout << ans << endl;




}