#include <bits/stdc++.h>
 
#define ll long long
#define lb lower_bound
#define pii pair<int,int>
#define pll pair<ll,ll>
#define F first
#define S second
#define ld long double
#define pb push_back
#define all(v) v.begin(),v.end()
#define in insert
#define sz(s) (int)s.size()
#define ppb pop_back
#define mem(a,i) memset(a,i,sizeof(a))
#define int ll

using namespace std;
 
const int MAX=700+10;
const int inf=2e18;
const int mod=1e9+7;

const int dx[4]={1,0,-1,0};
const int dy[4]={0,1,0,-1};

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

int n,k,s,t;
int x[MAX],y[MAX];
ld dp[MAX][MAX];

ld dist(ld a,ld b,ld c,ld d){
    return sqrt((a-c)*(a-c)+(b-d)*(b-d));
}

ld getY(ld X,ld Y){
    for(int i=0;i<=n;i++)for(int j=0;j<=k;j++)dp[i][j]=inf;
    dp[0][0]=0;
    for(int i=1;i<=n;i++){
        for(int j=0;j<=k;j++){
            dp[i][j]=dp[i-1][j];
            dp[i][j]=min(dp[i][j],max(dp[i-1][j-1],dist(X,Y,x[i],y[i])));
        }
    }
    return t*dp[n][k]+s*dist(0,0,X,Y);
}

ld get(ld x){
    ld l=-1e9,r=1e9;
    for(int i=1;i<=200;i++){
        ld m1=l+(r-l)/3,m2=r-(r-l)/3;
        if(getY(x,m1)<=getY(x,m2))r=m2;
        else l=m1;
    }
    return getY(x,l);
}

void solve(){
    cin>>k>>n>>s>>t;
    for(int i=1;i<=n;i++){
        cin>>x[i]>>y[i];
    }
    ld l=-1e9,r=1e9;
    for(int i=1;i<=200;i++){
        ld m1=l+(r-l)/3,m2=r-(r-l)/3;
        if(get(m1)<=get(m2))r=m2;
        else l=m1;
    }
    
    cout.precision(10);
    // for(int i=0;i<=10;i++)cout<<get(i)<<"\n";
    // cout<<fixed<<get(5)<<"\n";
    cout<<fixed<<get(l)<<"\n";
}

signed main(){
    // freopen("escape.in","r",stdin);
    // freopen("escape.out","w",stdout);
    ios_base::sync_with_stdio(0);
    // cin.tie(0);
    // cout.tie(0);
    int t=1;
    // cin>>t;
    while(t--)solve();
}