#include <iostream>
#include <algorithm>
#include <vector>
#include <cmath>
int main(){
	unsigned N,K,X,Y;
	std::cin>>N>>K>>X>>Y;
	std::vector<unsigned> A(N);
	int hp;
	for (unsigned i=0;i<N;i++){
		std::cin>>hp;
		A[i]=(unsigned)ceill((long double)(hp-1)/K);
	}
	unsigned long long UsedMp=0;
	std::sort(A.begin(),A.end(),std::greater<unsigned>());
	if(Y/X<(unsigned)A.size()){
		hp=A[Y/X];
		UsedMp+=A[Y/X]*Y;
	}else{
		hp=0;
	}
	for(unsigned i=0;i<N;i++){
		if(A[i]<=(unsigned)hp)break;
		UsedMp+=(A[i]-hp)*X;
	}
	std::cout<<UsedMp;
	return 0;
}