#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < n; i++)
using namespace std;

typedef long long ll;

int main() {
    ll N, K, X, Y;
    cin >> N >> K >> X >> Y;
    vector<ll> A(N);
    rep(i, N) {
        cin >> A[i];
        A[i]--;
    }
    sort(A.begin(), A.end());
    int lo = 0, hi = 1e9 + 1;
    while (lo + 1 < hi) {
        int mi = (lo + hi) / 2;
        int i = A.end() - upper_bound(A.begin(), A.end(), mi);
        //cout << "lo=" << lo << " hi=" << hi << " i=" << i << "\n";
        if (X * i < Y) hi = mi;
        else lo = mi;
    }
    //cout << lo << " " << hi << "\n";
    ll yn = (lo + K - 1) / K, ans = yn * Y;
    rep(i, N) {
        if (A[i] > yn * K) {
            ans += (A[i] - yn * K + K - 1) / K * X;
        }
    }
    cout << ans << "\n";
}