#define _GLIBCXX_DEBUG
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define ALL(v) v.begin(), v.end()
typedef long long ll;

template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }

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

int main(){
  int n,k,x,y;
  cin>>n>>k>>x>>y;
  
  int a;
  vector<int> A(n);
  int sum=0;
  rep(i,n){
    cin>>a;
    A[i]=(a-1+k-1)/k;
    sum+=(a-1+k-1)/k;
  }
  sort(ALL(A));
  
  int m;
  m=(y+x-1)/x;
  
  int sum1=0;
  if(n<m) cout<<sum<<endl;
  else{
    rep(i,n){
      if(A[i]>A[n-m]) sum1+=A[i]-A[n-m];
    }
    cout<<A[n-m]*y+sum1*x<<endl;
  }

  return 0;
}