#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(i, n) for(ll i = 0, i##_len = (n); i < i##_len; i++)
#define reps(i, s, n) for(ll i = (s), i##_len = (n); i < i##_len; i++)
#define rrep(i, n) for(ll i = (n) - 1; i >= 0; i--)
#define rreps(i, e, n) for(ll i = (n) - 1; i >= (e); i--)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define sz(x) ((ll)(x).size())
#define len(x) ((ll)(x).length())
#define endl "\n"

ll n, k, x, y;
vector<ll> a, rem;

ll f(ll ycnt) {
    ll ans = ycnt * y;
    rep(i, sz(rem)) ans += max(0LL, rem[i] - ycnt) * x;
    return ans;
}

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    // ifstream in("input.txt");
    // cin.rdbuf(in.rdbuf());
    cin >> n >> k >> x >> y;
    a.resize(n);
    rep(i, n) cin >> a[i];
    rem.resize(n);
    rep(i, n) rem[i] = (a[i] - 1 + (k - 1)) / k;
    ll low = 0, high = 1e9;
    while((low + 2) < high) {
        ll lm = (low * 2 + high) / 3;
        ll hm = (low + high * 2) / 3;
        if (f(lm) > f(hm)) {
            low = lm;
        }
        else {
            high = hm;
        }
    }
    ll mid = low + 1;
    cout << min(f(low), min(f(mid), f(high))) << endl;
    return 0;
}