#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <cmath>
using namespace std;
using ll = long long;

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

    int n, k, x, y;
    cin >> n >> k >> x >> y;

    vector<int> a(n);
    for (int i = 0; i < n; i++) {
        int t;
        cin >> t;
        a[i] = (t - 1 + (k - 1)) / k;
    }
    sort(a.begin(), a.end());

    ll r = 0;
    int p = 0;
    for (int i = 0; i < n; i++) {
        r += (a[i] - p) * min((n - i) * (ll)x, (ll)y);
        p = a[i];
    }

    cout << r << endl;

    return 0;
}