#include<stdio.h>
#include<iostream>
#include<algorithm>
#include<vector>
#include<string>
#include<utility>
#include<map>
#include<set>
#include<queue>
#include<stack>
#include<functional>
#include<math.h>
#include<random>
#include <bitset>
using namespace std;
#define N (1000000000+7)
//#define N 998244353
#define INF 1e16
typedef long long ll;
typedef pair<int,int> P;
typedef pair<int,P> Q;
typedef vector<ll> vec;
typedef vector<vec> mat;

const int inf = (int)1e9; 

int main(void){
	ll n,k,x,y;
	cin>>n>>k>>x>>y;
	vector<ll>a(n);
	for(int i=0;i<n;i++){
		cin>>a[i];
		a[i]--;
	}
	sort(a.begin(),a.end());
	ll ans = 0;
	ll HP = 0;
	for(int i=0;i<n;i++){
		if((n-i)*x>y){
			if(a[i]<=HP)continue;
			ll t = (a[i]-HP)/k + (((a[i]-HP)%k==0)?0:1);
			ans += t*y;
			HP += t*k;
		}
		else{
			if(a[i]<=HP)continue;
			else{
				ll t = (a[i]-HP)/k + (((a[i]-HP)%k==0)?0:1);
				ans+=t*x; 
			}
		}
		//cout<<ans<<" "<<HP<<endl;
	}
	cout<<ans<<endl;
	return 0;
}