#include <bits/stdc++.h>
using namespace std;
using ll = long long;
template <class T, class U> using Pa = pair<T, U>;
template <class T> using vec = vector<T>;
template <class T> using vvec = vector<vec<T>>;


int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    ll N,K,X,Y;
    cin >> N >> K >> X >> Y;
    vec<ll> B(N);
    for(int i=0;i<N;i++){
        int a;
        cin >> a;
        B[i] = (a+K-2)/K;
    }
    sort(B.begin(),B.end());
    vec<ll> R(N+1,0);
    for(int i=N-1;i>=0;i--) R[i] = R[i+1]+B[i];
    ll ans = R[0]*X;
    for(int i=0;i<N;i++){
        ll now = B[i]*Y+(R[i+1]-(N-1-i)*B[i])*X;
        ans = min(ans,now);
    }
    cout << ans << "\n";
}