#include <bits/stdc++.h>
using namespace std;
struct Point {
long double x, y;
};
// squared distance
long double dist2(const Point &a, const Point &b) {
long double dx = a.x - b.x;
long double dy = a.y - b.y;
return dx*dx + dy*dy;
}
// distance
long double dist(const Point &a, const Point &b) {
return sqrt(dist2(a,b));
}
// count how many points are inside or on the circle
long long count_inside(const Point &c, long double r, const vector<Point> &stars) {
const long double EPS = 1e-9;
long long cnt = 0;
long double rr = r*r;
for(auto &p : stars){
if(dist2(p, c) <= rr + EPS) cnt++;
}
return cnt;
}
// circumcircle of 3 points
bool circumcircle(const Point &A, const Point &B, const Point &C, Point ¢er, long double &r) {
long double ax = A.x, ay = A.y;
long double bx = B.x, by = B.y;
long double cx = C.x, cy = C.y;
long double d = 2*(ax*(by-cy) + bx*(cy-ay) + cx*(ay-by));
if(fabsl(d) < 1e-12) return false; // collinear
long double ux = ((ax*ax + ay*ay)*(by - cy) + (bx*bx + by*by)*(cy - ay) + (cx*cx + cy*cy)*(ay - by))/d;
long double uy = ((ax*ax + ay*ay)*(cx - bx) + (bx*bx + by*by)*(ax - cx) + (cx*cx + cy*cy)*(bx - ax))/d;
center = {ux, uy};
r = dist(center, A);
return true;
}
int main() {
long long n, k;
long double s, t;
cin >> k >> n >> s >> t;
vector<Point> stars(n);
for(long long i=0;i<n;i++){
cin >> stars[i].x >> stars[i].y;
}
long double ans = 1e30;
// k==1 case: radius 0 circle
if(k == 1){
for(auto &p : stars){
ans = min(ans, (long double)0.0);
}
}
// check all pairs
for(long long i=0;i<n-1;i++){
for(long long j=i+1;j<n;j++){
Point c = {(stars[i].x + stars[j].x)/2, (stars[i].y + stars[j].y)/2};
long double r = dist(stars[i], stars[j])/2;
if(count_inside(c, r, stars) >= k)
ans = min(ans, r);
}
}
// check all triples
for(long long i=0;i<n-2;i++){
for(long long j=i+1;j<n-1;j++){
for(long long l=j+1;l<n;l++){
Point c;
long double r;
if(!circumcircle(stars[i], stars[j], stars[l], c, r)) continue;
if(count_inside(c, r, stars) >= k)
ans = min(ans, r);
}
}
}
cout << fixed << setprecision(12) << ans*t << "\n";
}
