#include <bits/stdc++.h>
using namespace std;

#define ll long long
const int N=1e5+100;
ll n,m,x,y;
ll a[N];
ll ans;

int main()
{
    cin>>n>>m>>x>>y;
    for(int i=1;i<=n;i++)
    {
        cin>>a[i];
        a[i]--;
        if(a[i]%m==0) a[i]/=m;
        else a[i]=a[i]/m+1;
    }
    sort(a+1,a+1+n);
    int left=n,now=0;
    for(int i=1;i<=n;i++)
    {
        a[i]-=now;
        if(!a[i]) { left--;continue; }
        if((ll)left*x>y)
        {
            left--;
            now+=a[i];
            ans+=y*a[i];
        }
        else
        {
            left--;
            ans+=x*a[i];
        }
    }
    cout<<ans;
    return 0;
}