#include<bits/stdc++.h>
using namespace std;
#define double long double
mt19937 RAND(time(NULL));
int n,k;
double S,T,x[777],y[777],d[777],now,ans;
double Rand(){return (double)(RAND()%10001)/10000.0;}
int rnd(int l,int r){return RAND()%(r-l+1)+l;}
double dist(double x,double y,double xx,double yy){
	return sqrt((x-xx)*(x-xx)+(y-yy)*(y-yy));
}
double calc(double cx,double cy){
	for(int i=1;i<=n;i++)d[i]=dist(cx,cy,x[i],y[i]);
	nth_element(d+1,d+k,d+1+n);
	return d[k]*T+dist(cx,cy,0,0)*S;
}
void SA(double cx,double cy){
	for(double temp=1000000;temp>1e-9;temp*=0.99){
		double tx=rnd(-1000,1000)*temp;
		double ty=rnd(-1000,1000)*temp;
		cx+=tx;cy+=ty;
		auto ctmp=calc(cx,cy);
		if(ctmp<now||exp((now-ctmp)/temp)>=Rand())ans=min(ans,now=ctmp);
		else cx-=tx,cy-=ty;
	}
}
signed main(){
//	freopen("B.in","r",stdin);
//	freopen("B.out","w",stdout);
	ios::sync_with_stdio(0);
	cin.tie(0);cout.tie(0);
	cin>>k>>n>>S>>T;ans=9e18;
	for(int i=1;i<=n;i++)cin>>x[i]>>y[i];
	if(S>=1){
		while((double)clock()/CLOCKS_PER_SEC<=1)SA(0,0);
		for(int p=0;p<9;p++)
		while((double)clock()/CLOCKS_PER_SEC<=1+(p+1)*0.1)SA(rnd(-1e9,1e9),rnd(-1e9,1e9));
	}else{
		for(int p=0;p<19980;p++)
		while((double)clock()/CLOCKS_PER_SEC<=(p+1)*0.0001)
			SA(rnd(-1e9,1e9),rnd(-1e9,1e9));
	}
	cout<<fixed<<setprecision(12)<<ans<<endl;
	return 0;
}