/**
 *   @FileName	a.cpp
 *   @Author	kanpurin
 *   @Created	2020.06.05 21:46:51
**/

#include "bits/stdc++.h" 
using namespace std; 
typedef long long ll;

int main() {
    ll n, k, x, y;
    cin >> n >> k >> x >> y;
    vector< ll > a(n);
    for (int i = 0; i < n; i++) {
        cin >> a[i];
    }
    ll p = (y + x - 1) / x;
    ll ans = 0;
    sort(a.begin(), a.end());
    if (p <= 1) {
        cout << (a[n - 1] - 1 + k - 1) / k * y << endl;
        return 0;
    }
    if (p > n) {
        for (int i = 0; i < n; i++) {
            ans += (a[i] - 1 + k - 1) / k * x;
        }
        cout << ans << endl;
        return 0;
    }
    ll q = (a[n - p] - 1 + k - 1) / k;
    ans = (a[n - p] - 1 + k - 1) / k * y;
    for (int i = p; i < n; i++) {
        ans += (a[i] - 1 - q * k + k - 1) / k * x;
    }
    cout << ans << endl;
    return 0;
}