#include <bits/stdc++.h>
#define rep(i,n) for (int i = 0; i < (n); i ++)
using namespace std;
using ll = long long;
using PL = pair<ll,ll>;
using P = pair<int,int>;
constexpr int INF = 1000000000;
constexpr long long HINF = 1000000000000000;
constexpr long long MOD = 1000000007;
constexpr double EPS = 1e-4;
constexpr double PI = 3.14159265358979;

int main() {
    ll N,K,X,Y; cin >> N >> K >> X >> Y;
    vector<ll> A(N);
    rep(i,N) {
        cin >> A[i];
        A[i] --;
    }
    sort(A.begin(),A.end());
    int people = Y/X;

    ll ans = 0;
    if (people == 0) {
        ans = (A[N - 1] + K - 1)/K * Y;
        cout << ans << endl;
        return 0;
    }
    if (people >= N) {
        rep(i,N) ans += (A[i] + K - 1)/K * X;
        cout << ans << endl;
        return 0;
    }

    ll damage = (A[N - people - 1] + K - 1)/K * K;
    ans = (A[N - people - 1] + K - 1)/K * Y;
    for (int i = N - people;i < N;i ++) {
        if (A[i] - damage > 0) {
            ans += (A[i] - damage + K - 1)/K * X;
        }
    }
    cout << ans << endl; 
    return 0;
}