#include <bits/stdc++.h>
using namespace std;
using ld = long double;
int main() {
ios::sync_with_stdio(false);
cin.tie(NULL);
int k, n;
ld s, t;
cin >> k >> n >> s >> t;
vector<pair<ld, ld>> a(n);
for (int i = 0; i < n; i++) {
cin >> a[i].first >> a[i].second;
}
auto dist = [&](ld x1, ld y1, ld x2, ld y2) {
return sqrt((x1 - x2)*(x1 - x2) + (y1 - y2)*(y1 - y2));
};
ld ans = 1e18;
vector<pair<ld, ld>> candidates;
// 1. all stars as centers
for (auto &p : a) candidates.push_back(p);
// 2. midpoints of all pairs
for (int i = 0; i < n; i++) {
for (int j = i+1; j < n; j++) {
ld mx = (a[i].first + a[j].first) / 2.0;
ld my = (a[i].second + a[j].second) / 2.0;
candidates.push_back({mx, my});
}
}
// 3. also include origin (important!)
candidates.push_back({0, 0});
for (auto &c : candidates) {
vector<ld> dists;
for (auto &p : a) {
dists.push_back(dist(c.first, c.second, p.first, p.second));
}
sort(dists.begin(), dists.end());
ld r = dists[k-1]; // k-th closest star
ld move_cost = s * dist(0, 0, c.first, c.second);
ld build_cost = t * r;
ans = min(ans, move_cost + build_cost);
}
cout << fixed << setprecision(10) << (double)ans << "\n";
}
