/*** author: yuji9511 ***/
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using lpair = pair<ll, ll>;
const ll MOD = 1e9+7;
const ll INF = 1e18;
#define rep(i,m,n) for(ll i=(m);i<(n);i++)
#define rrep(i,m,n) for(ll i=(m);i>=(n);i--)
#define printa(x,n) for(ll i=0;i<n;i++){cout<<(x[i])<<" \n"[i==n-1];};
void print() {}
template <class H,class... T>
void print(H&& h, T&&... t){cout<<h<<" \n"[sizeof...(t)==0];print(forward<T>(t)...);}

void solve(){
    ll N,K,X,Y;
    cin >> N >> K >> X >> Y;
    ll A[100010];
    rep(i,0,N) cin >> A[i];
    ll num[100010] = {};
    rep(i,0,N) num[i] = (A[i] - 1 + K-1) / K;
    sort(num, num+N);
    ll cnt[100010] = {};
    cnt[N] = num[0];
    rep(i,1,N){
        if(num[i-1] != num[i]){
            ll diff = num[i] - num[i-1];
            cnt[N-i] = diff;
        }
    }
    ll ans = 0;
    rrep(i,N,0){
        if(cnt[i] == 0) continue;
        if(X * i < Y){
            ans += cnt[i] * X * i;
        }else{
            ans += cnt[i] * Y;
        }
    }
    print(ans);

}

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    solve();
}