#include <bits/stdc++.h>
using namespace std;
long double distance(pair<long double, long double> x, pair<long double, long double> y) {
long double dx = x.first - y.first;
long double dy = x.second - y.second;
return sqrt(dx*dx + dy*dy);
}
// Count how many points in z are inside circle centered at x with radius r
long long check(pair<long double, long double> x, long double r, const vector<pair<long double, long double>>& z) {
long long cnt = 0;
long double rr = r*r; // compare squared distances
for(auto &p : z){
long double dx = p.first - x.first;
long double dy = p.second - x.second;
if(dx*dx + dy*dy <= rr + 1e-9) cnt++;
}
return cnt;
}
// Compute circumcircle of 3 points
bool circumcircle(pair<long double,long double> A,
pair<long double,long double> B,
pair<long double,long double> C,
pair<long double,long double> ¢er,
long double &r)
{
long double ax=A.first, ay=A.second;
long double bx=B.first, by=B.second;
long double cx=C.first, cy=C.second;
long double d = 2*(ax*(by-cy) + bx*(cy-ay) + cx*(ay-by));
if(fabsl(d) < 1e-12) return false; // points collinear, no unique circle
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 = distance(center, A);
return true;
}
int main() {
long long n,k,i,j,l;
long double s,t;
cin >> k >> n >> s >> t;
vector<pair<long double,long double>> a;
for(i=1; i<=n; i++) {
long double b,c;
cin >> b >> c;
a.push_back({b,c});
}
long double ans = 1e30; // large initial value
// Pair case: circle diameter through two points
for(i=0; i<n-1; i++){
for(j=i+1; j<n; j++){
pair<long double,long double> c;
c.first = (a[i].first + a[j].first)/2;
c.second = (a[i].second + a[j].second)/2;
long double r = distance(a[i], a[j])/2;
if(check(c, r, a) >= k) {
ans = min(ans, r);
}
}
}
// Triple case: circle through 3 points
for(i=0; i<n-2; i++){
for(j=i+1; j<n-1; j++){
for(l=j+1; l<n; l++){
pair<long double,long double> c;
long double r;
if(!circumcircle(a[i], a[j], a[l], c, r)) continue;
if(check(c, r, a) >= k){
ans = min(ans, r);
}
}
}
}
cout << fixed << setprecision(12) << ans * t << endl;
}
