#include<iostream>
#include<algorithm>
using namespace std;
int N,K,X,Y;
long A[1<<17];
long LIM=2e18;
main()
{
	cin>>N>>K>>X>>Y;
	long S=0;
	for(int i=0;i<N;i++)
	{
		cin>>A[i];
		S+=A[i]=(A[i]-1+K-1)/K;
	}
	long ans;
	if(S<=LIM/X)ans=S*X;
	else ans=LIM;
	sort(A,A+N);
	long pre=0;
	for(int i=0;i<N;i++)
	{
		S-=(A[i]-pre)*(N-i);
		pre=A[i];
		if(S<=LIM/X)ans=min(ans,S*X+A[i]*Y);
	}
	cout<<ans<<endl;
}