#include <bits/stdc++.h>
using namespace std;
struct Point {
double x, y;
};
double dist(const Point &a, const Point &b) {
double dx = a.x - b.x, dy = a.y - b.y;
return sqrt(dx*dx + dy*dy);
}
// Circumcircle of 3 points
pair<Point, double> circumcircle(const Point &A, const Point &B, const Point &C) {
double a = B.x - A.x, b = B.y - A.y;
double c = C.x - A.x, d = C.y - A.y;
double e = a*(A.x+B.x) + b*(A.y+B.y);
double f = c*(A.x+C.x) + d*(A.y+C.y);
double det = 2*(a*(d)-b*(c));
if(fabs(det) < 1e-12) return {{0,0}, 1e18}; // degenerate
double cx = (d*e - b*f)/det;
double cy = (-c*e + a*f)/det;
Point center = {cx, cy};
double radius = dist(center, A);
return {center, radius};
}
// Circle from 2 points (two possible circles with given radius)
vector<pair<Point,double>> circlesFromPair(const Point &A, const Point &B) {
vector<pair<Point,double>> res;
double d = dist(A,B);
Point mid = {(A.x+B.x)/2, (A.y+B.y)/2};
double r = d/2;
double dx = (B.y - A.y)/d * r;
double dy = (A.x - B.x)/d * r;
// Two possible centers
res.push_back({{mid.x + dx, mid.y + dy}, r});
res.push_back({{mid.x - dx, mid.y - dy}, r});
return res;
}
int main() {
int k, n;
double s, f;
cin >> k >> n >> s >> f;
vector<Point> stars(n);
for(int i=0;i<n;i++) cin >> stars[i].x >> stars[i].y;
double best = 1e18;
const double eps = 1e-9;
// Single stars
for(int i=0;i<n;i++){
Point c = stars[i];
int cnt = 0;
for(int j=0;j<n;j++)
if(dist(c, stars[j]) <= eps) cnt++;
if(cnt >= k){
double cost = f*0 + s*dist({0,0}, c);
best = min(best, cost);
}
}
// Pairs
for(int i=0;i<n;i++){
for(int j=i+1;j<n;j++){
auto circles = circlesFromPair(stars[i], stars[j]);
for(auto &[c, r] : circles){
int cnt = 0;
for(int t=0;t<n;t++)
if(dist(c, stars[t]) <= r + eps) cnt++;
if(cnt >= k){
double cost = f*r + s*dist({0,0}, c);
best = min(best, cost);
}
}
}
}
// Triplets
for(int i=0;i<n;i++){
for(int j=i+1;j<n;j++){
for(int t=j+1;t<n;t++){
auto [c, r] = circumcircle(stars[i], stars[j], stars[t]);
if(r > 1e16) continue; // degenerate
int cnt = 0;
for(int p=0;p<n;p++)
if(dist(c, stars[p]) <= r + eps) cnt++;
if(cnt >= k){
double cost = f*r + s*dist({0,0}, c);
best = min(best, cost);
}
}
}
}
cout << fixed << setprecision(12) << best << "\n";
}
