#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);
	for(ll i = 0;i < n;++i) std::cin >> a[i];

	std::sort(a.begin(),a.end(),std::less<>());

	ll ans = 0;
	std::vector<ll> b(n,1);
	while(true)
	{
		bool out = true;
		ll m = 0;
		for(ll i = 0;i < n;++i)
			if(b[i] < a[i])
			{
				++m;
				out = false;
			}
		if(out) break;
		ll behoimi_cost = m*x;
		// ベホマラー
		if (y < behoimi_cost)
		{
			ans += y;
			for(ll i = 0;i < n;++i) b[i] += k;
		}
		// ベホイミ
		else
		{
			ans += x;
			for(ll i = 0;i < n;++i)
				if(b[i] < a[i]){ b[i] += k; break; }
		}
	}

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

	return 0;
}