#include <iostream>
#include <iomanip>
#include <vector>
#include <string>
#include <algorithm>
#include <cmath>
#include <map>
#include <unordered_map>
#include <queue>
#include <bitset>
#include <limits>

using ld = long double;
using ll = long long int;
using ul = unsigned long long int;

namespace lamlib
{
	/* constant */
	constexpr double epsilon = std::numeric_limits<double>::epsilon();

	/* math */
	template<class T> inline T abs(const T &a){ return (a>0) ? a : -a; }
	ul inline digit(const ul &num){ return static_cast<ul>(std::log10(num+epsilon))+1; }

	/* algorithm */
	ul gcd(const ul &a,const ul &b) { return (!b) ? a : gcd(b,a%b); } // NOTE: a > b
	std::vector<bool> eratosthenes(const ul &n)
	{
		std::vector<bool> prime_candidate(n,true);
		prime_candidate[0] = prime_candidate[1] = false;
		const ul max_n = static_cast<ul>(std::sqrt(n));
		for(ul i = 2;i < max_n;++i)
		{
			if(!prime_candidate[i]) continue;
			for(ul j = 2;i*j < n;++j) prime_candidate[i*j] = false;
		}
		return prime_candidate;
	}

	/* string */
	inline ul same_char_count(const std::string s,const char &ch){ return std::count(std::cbegin(s),std::cend(s),ch); }
}

// std::cout << std::fixed << std::setprecision(15) << std::endl;

int main(int argc,char *argv[])
{
	ll n,k,x,y;
	std::cin >> n >> k >> x >> y;

	std::vector<ll> a(n,0);
	std::vector<ll> need_recover(n,0);
	for(ll i = 0;i < n;++i)
	{
		std::cin >> a[i];
		ll cost = (a[i]-1)/k;
		need_recover[i] = ((a[i]-1)%k != 0) ? cost+1 : cost;
	}
	std::sort(need_recover.begin(),need_recover.end(),std::less<>());
	
	ll ans = 0;
	ll cast_count = 0;
	ll m = n;
	for(ll i = 0;i < n;++i)
	{
		need_recover[i] -= cast_count;
		--m;
		if(need_recover[i] <= 0) continue;
		// ベホマラー
		if(y < (m+1)*x)
		{
			ans += need_recover[i]*y;
			cast_count += need_recover[i];
		}
		// ベホイミ
		else
		{
			ans += need_recover[i]*x;
		}
	}

	std::cout << ans << std::endl;

	return 0;
}