#include <iostream>
int main(){
	unsigned N,K,X,Y;
	std::cin>>N>>K>>X>>Y;
	int *A=new int[N];
	int *NowHp=new int[N];
	for (int i=0;i<N;i++){
		std::cin>>A[i];
		NowHp[i]=1;
	}
	int finish=0,UsedMp=0;
	while(finish==0){
		int NeedHeal=0;
		for (int i=0;i<N;i++){
			if(NowHp[i]<A[i]){
				NeedHeal++;
			}
		}
		if(NeedHeal==0){
			finish++;
		}else if(NeedHeal*X<Y){
			for(int i=0;i<N;i++){
				while(NowHp[i]<A[i]){
					NowHp[i]+=K;
					UsedMp+=X;
				}
			}
			finish++;
		}else {
			for(int i=0;i<N;i++){
				NowHp[i]+=K;
			}
			UsedMp+=Y;
		}
	}
	std::cout<<UsedMp;
	return 0;
}