#include<bits/stdc++.h>
using namespace std;
#define Ll __int128
#define ll unsigned long long
int main()
{
    ll n,k,x,y;
    cin>>n>>k>>x>>y;
    ll a[n];
    vector<ll> v;
    for(int i=0; i<n; i++){
        cin>>a[i];
        v.push_back((a[i]-1+k-1)/k);
    }
    sort(v.begin(),v.end());
    ll ans=0;
    ll now=0;
    for(int i=0; i<n; i++){
        ll u=v[i];
        ans+=min(y,(n-i)*x)*(u-now);
        now=u;
    }
    cout<<ans<<endl;
}