#include <bits/stdc++.h>
#define all(x) (x).begin(), (x).end()
typedef long long ll;
#define MOD 998244353
using namespace std;
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];
    }
    sort(all(a), greater<ll>());
    ll m = y / x;
    ll y_num;
    if(m >= n) {
        y_num = 0;
    } else {
        y_num = (a[m] + k - 2) / k;
    }
    ll ans = y_num * y;
    for(int i = 0; i < n; i++) {
        ll tmp = (a[i] - y_num * k + k - 2) / k;
        ans += max(0LL, tmp) * x;
    }
    cout << ans << endl;
}