#include <bits/stdc++.h>
using namespace std;
template <class T>
inline int countbit(T n) {
  return (n == 0) ? 0 : (1 + countbit(n & (n - 1)));
}
template <class T>
inline T gcd(T a, T b) {
  return b ? gcd(b, a % b) : a;
}
const double EPS = 1e-9;
const double PI = acos(-1.0);
pair<int, int> arr[101];
int xx0, yy0;
int N;
pair<double, double> arrT[101];
int cant;
int K;
double eps;
double dp[101][101];
double RR;
int rep[101];
int paso;
double dist(double x1, double y1, double x2, double y2) {
  return (x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2);
}
double prob(int ind, int quedan) {
  if (quedan <= 0) return 1.;
  if (ind == cant) return 0.;
  double& res = dp[ind][quedan];
  if (res >= -0.1) return res;
  res = 0.;
  res += prob(ind + 1, quedan - 1) *
         exp(1. - dist(xx0, yy0, arrT[ind].first, arrT[ind].second) / (RR));
  res +=
      prob(ind + 1, quedan) *
      (1. - exp(1. - dist(xx0, yy0, arrT[ind].first, arrT[ind].second) / (RR)));
  return res;
}
bool ok(double R) {
  RR = R * R;
  cant = 0;
  int tot = 0;
  for (int i = 0; i < N; i++) {
    if (RR < dist(xx0, yy0, arr[i].first, arr[i].second))
      arrT[cant++] = arr[i];
    else
      tot += 1;
  }
  if (tot >= K) return true;
  memset(dp, -1, sizeof(dp));
  return prob(0, K - tot) > 1. - eps;
}
int main() {
  int i, j, k;
  cin >> N;
  cin >> K >> eps;
  eps /= 1000.;
  cin >> xx0 >> yy0;
  map<pair<int, int>, int> seen;
  for (i = 0; i < N; i++) {
    int x, y;
    cin >> x >> y;
    arr[i] = make_pair(x, y);
    seen[arr[i]]++;
  }
  if (seen[make_pair(xx0, yy0)] >= K) {
    cout << 0. << endl;
    return 0;
  }
  double b = 0., e = 10000.;
  sort(arr, arr + N);
  for (k = 0; k < N; k++)
    for (i = 0; i + 1 < N; i++)
      if (dist(xx0, yy0, arr[i].first, arr[i].second) >
          dist(xx0, yy0, arr[1 + i].first, arr[1 + i].second))
        swap(arr[i], arr[i + 1]);
  for (paso = 0; paso < 100 && (e - b) > 1e-12; paso++) {
    double med = (e + b) / 2.;
    if (ok(med))
      e = med;
    else
      b = med;
  }
  printf("%.12lf\n", e);
  return 0;
}
