#include <iostream>
#include <algorithm>
#include <vector>

using lint = long long;

void solve() {
    int n;
    lint k, x, y;
    std::cin >> n >> k >> x >> y;

    std::vector<lint> ps(n);
    for (auto& p : ps) {
        lint a;
        std::cin >> a;
        p = (a - 1 + k - 1) / k;
    }
    std::sort(ps.begin(), ps.end());

    lint ans = 0, done = 0;
    for (int i = 0; i < n; ++i) {
        lint need = ps[i] - done;
        lint m = n - i;
        ans += std::min(m * x, y) * need;
        done = ps[i];
    }

    std::cout << ans << "\n";
}

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

    solve();

    return 0;
}