#include <bits/stdc++.h>
using namespace std;
template <class T>
inline vector<T> split(string x) {
  vector<T> r;
  stringstream ss(x);
  T t;
  while (ss >> t) r.push_back(t);
  return r;
}
pair<int, int> pos[1000];
double boom[1000];
double dp[101][101];
int main() {
  int n, obj, x, y;
  double prob;
  scanf("%d", &n);
  int temp;
  scanf("%d %d", &obj, &temp);
  prob = (double)temp / 1000.0;
  scanf("%d %d", &x, &y);
  for (int i = 0; i < n; i++) {
    scanf("%d %d", &pos[i].first, &pos[i].second);
  }
  double low = 0.0, high = 135456445665.0, mid;
  for (int k = 0; k < 200; k++) {
    mid = (low + high) / 2.0;
    int cnt = 0;
    vector<double> vvv;
    for (int j = 0; j < n; j++) {
      double dist = hypot(x - pos[j].first, y - pos[j].second);
      if (dist * dist <= mid * mid) {
        boom[j] = 1.0;
      } else {
        boom[j] =
            pow(2.71828182845904523536, 1.0 - ((dist / mid) * (dist / mid)));
      }
    }
    memset(dp, 0, sizeof(dp));
    dp[0][0] = 1.0;
    for (int i = 1; i <= n; i++) {
      dp[i][0] = dp[i - 1][0] * (1.0 - boom[i - 1]);
    }
    for (int i = 1; i <= n; i++) {
      for (int j = 1; j <= i; j++) {
        dp[i][j] =
            dp[i - 1][j] * (1 - boom[i - 1]) + dp[i - 1][j - 1] * boom[i - 1];
      }
    }
    double sum = 0.0;
    for (int i = obj; i <= n; i++) {
      sum += dp[n][i];
    }
    if (1.0 - sum <= prob) {
      high = mid;
    } else {
      low = mid;
    }
  }
  printf("%.15lf\n", mid);
  return 0;
}
