#include <bits/stdc++.h>
#include <iomanip>
using namespace std;
#define reps(i,s,n) for(int i = s; i < n; i++)
#define rep(i,n) reps(i,0,n)
#define Rreps(i,n,e) for(int i = n - 1; i >= e; --i)
#define Rrep(i,n) Rreps(i,n,0)
#define ALL(a) a.begin(), a.end()
#define fi first
#define se second
typedef long long ll;
typedef vector<ll> vec;
typedef vector<vec> mat;

ll N,M,H,W,Q,K,A,B;
string S;
const ll MOD = 998244353;
//const ll MOD = (1e+9) + 7;
typedef pair<ll, ll> P;
const ll INF = (1LL<<62);
template<class T> bool chmin(T &a, const T &b){
    if(a > b) {a = b; return true;}
    else return false;
}
template<class T> bool chmax(T &a, const T &b){
    if(a < b) {a = b; return true;}
    else return false;
}

int main() {
    ll X, Y;
    cin>>N>>K>>X>>Y;
    vec a(N);
    rep(i,N) {
        cin>>a[i];
        --a[i];
    }
    sort(ALL(a));
    ll ans = ((*max_element(ALL(a)) + K - 1) / K) * Y;
    ll num = 0, temp = 0;
    rep(i,N) num += (a[i] + K - 1) / K;
    rep(i,N){
        chmin(ans, num * X + temp * Y);
        ll next_up = (a[i] + K - 1) / K - temp;
        num -= (N - i) * next_up;
        temp += next_up;
    }
    cout<<ans<<endl;
}