#include <bits/stdc++.h>
#define rep(i,n) for(ll i=0;i<(ll)(n);i++)
using namespace std;
using ll = long long ;
using P = pair<int,int> ;
using pll = pair<long long,long long>;
constexpr int INF = 1e9;
constexpr long long LINF = 1e17;
constexpr int MOD = 1000000007;
constexpr double PI = 3.14159265358979323846;

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

    ll ans = 0;
    ll mx = 0;
    rep(i,n){
        if((n-i)*x >= y){
            ans += y * (a[i] - mx);
            mx = a[i];
        }else{
            ans += x * (a[i] - mx);
        }
    }
    cout << ans << endl;
    return 0;
}