#include <bits/stdc++.h>  // clang-format off
using Int = long long;
#define REP_(i, a_, b_, a, b, ...) for (Int i = (a), lim##i = (b); i < lim##i; i++)
#define REP(i, ...) REP_(i, __VA_ARGS__, __VA_ARGS__, 0, __VA_ARGS__)
struct SetupIO { SetupIO() { std::cin.tie(nullptr), std::ios::sync_with_stdio(false), std::cout << std::fixed << std::setprecision(13); } } setup_io;
#ifndef dump
#define dump(...)
#endif  // clang-format on

/**
 *    author:  knshnb
 *    created: Fri Jun  5 21:50:10 JST 2020
 **/

signed main() {
    Int n, K, X, Y;
    std::cin >> n >> K >> X >> Y;
    std::vector<Int> a(n);
    REP(i, n) std::cin >> a[i], a[i] = (a[i] - 1 + K - 1) / K;
    std::sort(a.rbegin(), a.rend());
    a.push_back(0);
    Int minus = a[std::min(Y / X, n)];
    Int ans = Y * minus;
    REP(i, n) {
        ans += X * std::max(0LL, a[i] - minus);
    }
    std::cout << ans << std::endl;
}