#include <bits/stdc++.h>
using namespace std;
const double EPS = 1e-10;
const double PI = acos(-1.0);
template <class T>
T gcd(T a, T b) {
  for (T c; b; c = a, a = b, b = c % b)
    ;
  return a;
}
template <class T>
void out(const vector<T> &a) {
  for (int i = 0; i < ((int)(a).size()); ++i) cout << a[i] << " ";
  cout << endl;
}
int countbit(int n) { return n == 0 ? 0 : 1 + countbit(n & (n - 1)); }
const int d8[8][2] = {{1, 0}, {-1, 0},  {0, 1},  {0, -1},
                      {1, 1}, {-1, -1}, {1, -1}, {-1, 1}};
const int d4[4][2] = {{1, 0}, {-1, 0}, {0, 1}, {0, -1}};
inline int dcmp(double x) { return (x > EPS) - (x < -EPS); }
inline double cross(const complex<double> &a, const complex<double> &b) {
  return (conj(a) * b).imag();
}
inline double dot(const complex<double> &a, const complex<double> &b) {
  return (conj(a) * b).real();
}
double f(double D, double R) {
  if (dcmp(R) == 0) {
    if (dcmp(D) == 0) return 1.0;
    return 0.0;
  }
  if (dcmp(D - R) <= 0) return 1.0;
  return exp(1 - ((D / R) * (D / R)));
}
const int N = 110;
double a[N], p[N];
double C[N][N];
double dp[N];
int main() {
  for (int i = 0; i < N; ++i) {
    C[i][i] = C[i][0] = 1.0;
    for (int j = 1; j < i; ++j) C[i][j] = C[i - 1][j - 1] + C[i - 1][j];
  }
  int n, m;
  double x, y, x2, y2, eps;
  scanf("%d", &n);
  scanf("%d %lf", &m, &eps);
  eps /= 1000;
  scanf("%lf %lf", &x, &y);
  for (int i = 0; i < n; ++i) {
    scanf("%lf %lf", &x2, &y2);
    a[i] = sqrt(((x - x2) * (x - x2)) + ((y - y2) * (y - y2)));
  }
  double low, high, mid;
  for (low = 0.0, high = 4e3; high - low > 1e-7;) {
    mid = (low + high) / 2;
    for (int i = 0; i < n; ++i) p[i] = f(a[i], mid);
    fill(dp, dp + n + 1, 0.0);
    dp[0] = 1.0;
    for (int i = 0; i < n; ++i) {
      for (int j = n; j > 0; --j) dp[j] = dp[j - 1] * p[i] + dp[j] * (1 - p[i]);
      dp[0] = dp[0] * (1 - p[i]);
    }
    double sum = 0.0;
    for (int i = m; i <= n; ++i) sum += dp[i];
    if (1 - sum <= eps)
      high = mid;
    else
      low = mid;
  }
  printf("%.10f\n", high);
  return 0;
}
