#include <bits/stdc++.h>
#define int long long
#define endl '\n'
#define FOR(i, a, n) for (int i = (a); i < (n); ++i)
#define REP(i, n) FOR(i, 0, n)
using namespace std;

void _main() {
    int N, K, X, Y;
    cin >> N >> K >> X >> Y;
    vector<int> A(N);
    for (int i = 0; i < N; ++i) {
        cin >> A[i];
    }
    int ans = 0;
    if (Y > N * X) {
        for (int i = 0; i < N; ++i) {
            ans += (A[i] + K - 2) / K;
        }
        cout << ans << endl;
    } else {
        vector<int> B(N);
        for (int i = 0; i < N; ++i) {
            B[i] = (A[i] + K - 2) / K;
        }
        sort(B.begin(), B.end());
        int pre = 0, l = 0;
        while (true) {
            while (l < N && B[l] == pre) l++;
            if (l == N) break;
            int num = N - l;
            ans += min(Y, X * num) * (B[l] - pre);
            pre = B[l];
        }
        cout << ans << endl;
    }
}

signed main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout << fixed << setprecision(10);
    _main();
    return 0;
}