#include <bits/stdc++.h>
using namespace std;
#define modulo 1000000007
#define mod(mod_x) ((((long long)mod_x+modulo))%modulo)
#define Inf 1000000000000000010



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

	long long ans  = Inf;
	if(S.back()<=1000000001)ans = S.back()*X;
	
	for(int i=0;i<N;i++){
		long long t = A[i]*Y;
		long long x = (S.back()-S[i+1] - (N-1-i)*A[i]);
		if(x>=1000000001)continue;
		t += x*X;
		ans = min(ans,t);
	}
	cout<<ans<<endl;
	
	return 0;
}