#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); i++)
using namespace std;
typedef long long ll;

int main(){
    cin.tie(0);
    ios::sync_with_stdio(0);
    
    ll N,K,X,Y; cin >> N >> K >> X >> Y;
    vector<ll> C(N);
    rep(i,N) {
        ll a; cin >> a;
        C[i] = (a - 1 + K - 1) / K;
    }

    sort(C.begin(), C.end());
    ll ans = 0, sum = 0;
    rep(i,N) {
        C[i] -= sum;
        if(__int128_t(X) * C[i] * (N - i) <= Y * C[i]) {
            ans += X * C[i];
        } else {
            ans += Y * C[i];
            sum += C[i];
        }
    }

    cout << ans << endl;
}