#include <bits/stdc++.h>
using namespace std;
using ll=long long;
using vin=vector<int>;
using vll=vector<long long>;
using vvin=vector<vector<int>>;
using vvll=vector<vector<long long>>;
using vstr=vector<string>;
using vvstr=vector<vector<string>>;
using vch=vector<char>;
using vvch=vector<vector<char>>;
using vbo=vector<bool>;
using vvbo=vector<vector<bool>>;
using vpii=vector<pair<int,int>>;
using pqsin=priority_queue<int,vector<int>,greater<int>>;
#define mp make_pair
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define rep2(i,s,n) for(int i=(s);i<(int)(n);i++)
#define all(v) v.begin(),v.end()
#define decp(n) cout<<fixed<<setprecision((int)n)
const int inf=1e9+7;
const ll INF=1e18;

int main(){
    int n,k,x,y;cin>>n>>k>>x>>y;
    vll a(n);rep(i,n){
        cin>>a[i];
        a[i]--;
    }
    ll tmp=y/x;
    sort(all(a));
    ll sum=0;
    if(n-tmp>0){
        ll num=(a[n-tmp-1]+k-1)/k;
        sum+=num*y;
        rep(i,n)a[i]-=num*k;
        rep(i,n)if(a[i]>0)sum+=((a[i]+k-1)/k)*x;
    }
    else rep(i,n)sum+=((a[i]+k-1)/k)*x;
    cout<<sum<<endl;
}