#include <bits/stdc++.h>
using namespace std;
double dp[110][110];
int n, np, ep, x[110], y[110], xint, yint;
double dis(int i) {
  return sqrt((x[i] - xint) * 1.0 * (x[i] - xint) +
              (y[i] - yint) * 1.0 * (y[i] - yint));
}
double prob(double d, double r) {
  if (d <= r) return 1.0;
  return exp(1.0 - (d / r) * (d / r));
}
int main(int argc, char const *argv[]) {
  double l = 0.0, r = (double)1e15;
  double mid;
  cin >> n >> np >> ep;
  cin >> xint >> yint;
  double take = (double)ep / 1000.0;
  for (int i = 1; i <= n; i++) cin >> x[i] >> y[i];
  for (int i = 0; i < 200; i++) {
    mid = (l + r) * 0.5;
    dp[0][0] = 1.0;
    for (int k = 1; k <= n; k++)
      for (int j = 0; j <= n; j++) dp[k][j] = 0.0;
    for (int j = 1; j <= n; j++) {
      for (int k = 0; k <= j; k++) {
        double p = prob(dis(j), mid);
        if (k == 0)
          dp[j][k] += (dp[j - 1][k] * (1.0 - p));
        else
          dp[j][k] += (dp[j - 1][k - 1] * p + dp[j - 1][k] * (1.0 - p));
      }
    }
    double hold = 0.0;
    for (int j = 0; j < np; j++) {
      hold += dp[n][j];
    }
    if (hold <= take) {
      r = mid;
    } else {
      l = mid;
    }
  }
  mid = (l + r) * 0.5;
  printf("%.15f\n", mid);
  return 0;
}
