#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;
long long a[100010], m[100010], z = 0;
int main() {
	long long n, k, x, y;
	cin >> n >> k >> x >> y;
	long long l = y / x;
	for (int i = 0; i < n; i++) {
		cin >> a[i];
		a[i]--;
		m[i] = (a[i] + k - 1) / k;
	}
	sort(a, a + n);
	sort(m, m + n);
	long long ans = 0, r = 0;
	if (n - l - 1 >= 0) {
		ans += m[n - l - 1] * y;
		r = m[n - l - 1];
	}
	for (int i = max(z, n - l); i < n; i++) {
		ans += (m[i] - r) * x;
	}
	cout << ans << endl;
}