#include <bits/stdc++.h>
using namespace std;
int n, k;
double x[200], y[200], X, Y, eps;
double f(double radius) {
  double p[200];
  for (int i = 1; i <= n; i++) {
    double D = sqrt((x[i] - X) * (x[i] - X) + (y[i] - Y) * (y[i] - Y));
    if (radius - D >= 1e-9)
      p[i] = 1.0;
    else {
      if (radius < 1e-9)
        p[i] = 0.0;
      else
        p[i] = exp(1 - D * D / radius / radius);
    };
  }
  double dp[200][200];
  memset(dp, 0, sizeof(dp));
  dp[1][0] = 1 - p[1];
  dp[1][1] = p[1];
  for (int i = 2; i <= n; i++)
    for (int j = 0; j <= i + 1; j++) {
      if (j) dp[i][j] += dp[i - 1][j - 1] * p[i];
      dp[i][j] += dp[i - 1][j] * (1 - p[i]);
    };
  double answer = 0;
  for (int i = 0; i < k; i++) answer += dp[n][i];
  return answer;
};
int main() {
  scanf("%d%d%lf%lf%lf", &n, &k, &eps, &X, &Y);
  for (int i = 1; i <= n; i++) scanf("%lf%lf", &x[i], &y[i]);
  double r_low = 0.0, r_top = 10000.0, r_mid;
  for (int its = 1; its <= 100; its++) {
    r_mid = (r_low + r_top) / 2.0;
    if (eps * 0.001 - f(r_mid) >= 1e-9)
      r_top = r_mid;
    else
      r_low = r_mid;
  };
  printf("%0.10lf\n", (r_top + r_low) / 2.0);
  return 0;
}
