#include<bits/stdc++.h>

using namespace std;
using ll=long long;
#define rep2(i, a, n) for(int i = (a); i < (n); i++)
#define rep(i, n) rep2(i,0,n)
#define inp(...) __VA_ARGS__; in(__VA_ARGS__)
#define ot(...) __VA_ARGS__; out(__VA_ARGS__)

void in() {} template <typename Head, typename... Tail> void in(Head&& head, Tail&&... tail) { cin>>head; in(forward<Tail>(tail)...); }
void out() {} template <typename Head, typename... Tail> void out(Head&& head, Tail&&... tail) { cout<<head<<endl; out(forward<Tail>(tail)...); }

int main(){
  cin.tie(nullptr);ios_base::sync_with_stdio(false);
  ll inp(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 wd=n;
  while(wd*x>=y)wd--;
  ll all;
  if(wd==n)all=0;
  else all=(a[n-wd-1]+k-1)/k;
  ll ans=all*y;
  rep(i,wd){
    ans+=(((a[n-wd+i]-all*k)+k-1)/k)*x;
  }
  cout<<ans<<endl;
}