#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;
using int64 = long long;

int main() {
    int64 n,k,x,y;
    cin >> n >> k >> x >> y;

    vector a(n,0LL);
    for (int i=0; i<n; i++) {
        cin >> a[i];
        a[i]--;
    }

    sort(a.rbegin(), a.rend());

    int64 ans = 0;
    int64 cnt = 0;
    while(!empty(a)) {
        if (a.size()*x >= y) {
            int64 e = (a.back()-cnt*k+k-1) / k;
            ans += y * e;
            cnt += e;
            while(!empty(a) && a.back() - cnt*k <= 0)
                a.pop_back();
        } else {
            int64 e = (a.back() - cnt*k +k-1) / k;
            ans += x * e;
            a.pop_back();
        }
    }

    cout << ans << endl;
}