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

int main()
{
	int N;
	long long K, X, Y;
	cin >> N >> K >> X >> Y;
	vector<long long> a( N );
	for( int i = 0; i < N; i++ ) {
		long long A;
		cin >> A;
		a[i] = (A - 1 + K - 1) / K;
	}

	sort( a.begin(), a.end() );
	vector<pair<long long, int>> p;
	int n = 0;
	for( int i = 0; i < N; i++ ) {
		if( i + 1 < N && a[i] == a[i + 1] ) {
			n++;
		}
		else {
			p.push_back( make_pair( a[i], n + 1 ) );
			n = 0;
		}
	}
	n = N;
	for( int i = 0; i < p.size(); i++ ) {
		long long s = p[i].second;
		p[i].second = n;
		n -= s;
	}
	long long ans = 0;
	long long last = 0;
	for( int i = 0; i < p.size(); i++ ) {
		int n = p[i].second;
		long long h = p[i].first - last;
		if( n * X < Y ) ans += n * X * h;
		else ans += Y * h;
		last = p[i].first;
	}

	cout << ans << endl;
}