#include<iostream>
#include<vector>
#include<string>
#include<algorithm>
#include<map>
#include<cmath>
#include<queue>
#include<stack>
#include<list>

#define endl "\n"
using namespace std;
using ll = long long;
const ll MOD = 1e9+7;
const ll INF = 1e18;
#define REP(i, n) for(int i = 0; i < n; i++)
using Graph = vector<vector<int>>;

int main(){
    ll n,k,x,y;
    cin>>n>>k>>x>>y;
    vector<ll> a(n),b(n);
    for(ll i=0;i<n;i++){
        cin>>a[i];
        b[i] = (a[i]-1 +k-1) / k;
    }
    sort(b.begin(),b.end(),greater<ll>());

    ll ans = 0;
    ll r = y / x;
    if(r < n){
        ans += y * b[r];
        for(ll i=0;i<r;i++){
            ans += x * (b[i] - b[r]);
        }
    }
    else{
        for(ll i=0;i<n;i++){
            ans += x * b[i];
        }
    }

    cout<<ans<<endl;
}