#include <iostream>
#include <vector>
#include <algorithm>
#include <map>
#include <queue>
#include <cstdio>
#include <set>
using namespace std;
typedef long long int ll;

int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    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]--;
        a[i]=(a[i]+k-1)/k;
    }
    ll res=0;
    sort(a.begin(), a.end());
    ll cnt=0;
    for(int i=0;i<n;i++){
        if((n-i)*x>y){
            res+=(a[i]-cnt)*y;
            cnt=a[i];
        }
        else{
            res+=(a[i]-cnt)*x;
        }
    }
    cout << res << endl;
}