#include <bits/stdc++.h>
using namespace std;

#define int long long
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }

signed main(){
	int n, k, x, y;
	cin >> n >> k >> x >> y;

	int a[100010];
	for(int i = 0;i < n;i++){
		cin >> a[i];
		a[i]--;
	}

	int m = n;
	map<int, int> mp;

	int cnt = 0;
	for(int i = 0;i < n;i++){
		int tmp = (a[i]+k-1)/k;
		mp[tmp]++; 
		cnt += tmp;
	}

	int ans = cnt * x;

	int old = 0;
	int yy = 0;
	for(auto e : mp){
		cnt -= m * (e.first-old);
		old = e.first;
		m -= e.second;
		chmin(ans, x*cnt + y*e.first);
	}

	cout << ans << endl;

	return 0;
}