#pragma GCC optimize("Ofast")
#pragma GCC target("avx2")

#define getrp() ({char*mmap();mmap(0l,1l<<25,1,2,0,0ll);})
#define rd() ({int _v=0,_c;while(_c=*rp++-48,_c>=0)_v=_v*10+_c;_v;})
#define wt(v) ({ulong _z=v;do*--wp=_z%10+48;while(_z/=10);})
#define wt1(v) ({char wbuf[64],*wp=wbuf+sizeof wbuf;wt(v);write(1,wp,wbuf+sizeof wbuf-wp);})
#define rep(v,e) for(typeof(e) v=0;v<e;++v)
#define rep3(v,s,e) for(typeof(e) v=s;v<e;++v)
#define max(a,b) (a>=b?a:b)

typedef unsigned long ulong;

void sort_aux(unsigned*a,unsigned*b,int n){
	int c[256];
	for(int i=0;i<256;++i){
		c[i]=0;
	}
	for(int i=0;i<n;++i){
		++c[a[i]&255];
	}
	int t=0;
	for(int i=0;i<256;++i){
		int u=c[i];
		c[i]=t;
		t+=u;
	}
	for(int i=0;i<n;++i){
		b[c[a[i]&255]++]=a[i]>>8|a[i]<<24;
	}
}

void sort(unsigned*a,int n){
	unsigned*b=a+n;
	sort_aux(a,b,n);
	sort_aux(b,a,n);
	sort_aux(a,b,n);
	sort_aux(b,a,n);
}

unsigned a[100000*2];

int main(){
	char*rp=getrp();
	int n=rd();
	int k=rd();
	int x=rd();
	int y=rd();
	rep(i,n){
		a[i]=rd();
	}
	sort(a,n);
	int b=max(0,n-y/x);
	ulong z=0;
	rep3(i,b,n){
		z+=(a[i]+k-2)/k;
	}
	wt1(z*x+(b?(a[b-1]+k-2)/k*(y-(ulong)x*(n-b)):0));
	_exit(0);
}