#include <iostream>
#include <string>
#include <algorithm>
#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <iomanip>
#include <cmath>
#include <stdio.h>
#include <queue>
#include <deque>
#include <cstdio>
#include <set>
#include <map>
#include <bitset>
#include <stack>
#include <cctype>
using namespace std;
int main() {
#define int long long
	long long n, k, x, y;
	cin >> n >> k >> x >> y;
	vector<int> vec;
	for (int i = 0; i < n; i++) {
		long long a;
		cin >> a;
		a--;
		if (a != 0) {
			vec.emplace_back((a + k - 1) / k);
		}
	}
	long long z;
	if (vec.empty()) {
		cout << "0" << endl;
		return 0;
	}
	sort(vec.begin(), vec.end());
	for (int i = n; i >= 0; i--) {
		if (y > x * i) {
			z = i;
			break;
		}
	}
	long long ans = 0;
	long long o;
	if (n - z - 1 != -1) {
		ans += vec[n - z - 1] * y;
		o = vec[n - z - 1];
	}
	else {
		o = 0;
	}
	for (int i = n - z; i < n; i++) {
		ans += (vec[i] - o) * x;
	}
	cout << ans << endl;
	return 0;
}