#include <iostream>
#include <vector>
#include <algorithm>
#include <functional>
#include <cassert>

using namespace std;
#define rep(i,n) for(int i=0;i<(n);i++)
int main() {
	long long N, K, X, Y;
	cin >> N >> K >> X >> Y;

	vector<long long> A(N, 0);
	int Max = 0;

	rep(i, N) {
		cin >> A.at(i);
		A.at(i)--;
		if (A.at(i) > Max) {
			Max = A.at(i);
		}
	}

	long long ans = 0;

	int S = Y / X;

	long long ZERO = 0;

	if (S >= N) {
		rep(i, N) {
			ans += ((A.at(i) + K - 1) / K)*X;
		}
	}
	else if (S < 1) {
		ans= ((Max + K - 1) / K) * Y;
	}
	else {
		sort(A.begin(),A.end());
		long long beho1 =( (A.at(N - S -1) + K - 1) / K);
		rep(i, N) {
			A.at(i) =std::max(A.at(i)-beho1 * K,ZERO);
		}
		rep(i, N) {
			ans += ((A.at(i) + K - 1) / K) * X;
		}
		ans += beho1 * Y;
	}

	cout << ans << endl;
}