#include <iostream>
#include <cstdio>
#include <cmath>
#include <ctime>
#include <cstdlib>
#include <cassert>
#include <vector>
#include <list>
#include <stack>
#include <queue>
#include <deque>
#include <map>
#include <set>
#include <bitset>
#include <string>
#include <algorithm>
#include <utility>
#define llint long long
#define inf 1e18
#define rep(x, s, t) for(llint (x) = (s); (x) < (t); (x)++)
#define Rep(x, s, t) for(llint (x) = (s); (x) <= (t); (x)++)
#define chmin(x, y) (x) = min((x), (y))
#define chmax(x, y) (x) = max((x), (y))

using namespace std;
typedef pair<llint, llint> P;

llint n, k, x, y;
llint a[100005];

int main(void)
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	
	cin >> n >> k >> x >> y;
	llint h;
	for(int i = 1; i <= n; i++){
		cin >> h;
		h--;
		a[i] = (h+k-1)/k;
	}
	sort(a+1, a+n+1);
	
	llint ans = inf*2, sum = 0;
	for(int i = n; i >= 0; i--){
		if((sum-a[i]*(n-i)) <= ((llint)inf)/x){
			ans = min(ans, a[i]*y + (sum-a[i]*(n-i))*x);
			sum += a[i];
		}
	}
	cout << ans << endl;
	
	return 0;
}