#include <cstdio>
#include <cstring>
#include <iostream>
#include <string>
#include <cmath>
#include <bitset>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <algorithm>
#include <complex>
#include <unordered_map>
#include <unordered_set>
#include <random>
#include <cassert>
#include <fstream>
#include <utility>
#include <functional>
#include <time.h>
#include <stack>
#include <array>
#include <list>
#define popcount __builtin_popcount
using namespace std;
typedef long long int ll;
typedef pair<int, int> P;

int main()
{
    int n; ll k, x, y;
    cin>>n>>k>>x>>y;
    ll a[100010];
    for(int i=0; i<n; i++){
        cin>>a[i];
        a[i]=(a[i]-1+k-1)/k;
    }
    ll m=min((y+x-1)/x, (ll)n+1);
    sort(a, a+n);
    ll t=0;
    if(n-m>=0) t=a[n-m];
    ll ans=y*t;
    for(int i=n-m+1; i<n; i++) ans+=x*(a[i]-t);
    cout<<ans<<endl;
    return 0;
}