#include <bits/stdc++.h>
using namespace std;
const double eps = 1e-8;
const double eee = 2.7182818284590452353602874713527;
double d[110];
double dp[110][110];
int n, k, e;
double dist(double a, double b, double c, double d) {
  double x = c - a;
  double y = d - b;
  x *= x;
  y *= y;
  return sqrt(x + y);
}
double exp(int i, double x) {
  if (d[i] <= x + eps) return 1.0;
  return pow(eee, 1 - d[i] * d[i] / (x * x));
}
bool sol(double x) {
  memset(dp, 0, sizeof(dp));
  dp[0][0] = 1;
  for (int i = 1; i <= n; ++i) {
    dp[i][0] = 1;
    for (int j = 1; j <= i; ++j) {
      double p = exp(i, x);
      dp[i][j] = dp[i - 1][j] * (1 - p) + dp[i - 1][j - 1] * p;
    }
  }
  if (dp[n][k] * 1000 >= 1000 - e) {
    return true;
  } else {
    return false;
  }
}
double cal(double l, double r) {
  double mid;
  mid = (l + r) / 2;
  while (r - l > eps) {
    mid = (l + r) / 2;
    if (sol(mid)) {
      r = mid;
    } else {
      l = mid;
    }
  }
  return mid;
}
int main() {
  double x0, y0;
  while (scanf("%d", &n) != EOF) {
    scanf("%d%d", &k, &e);
    scanf("%lf%lf", &x0, &y0);
    for (int i = 1; i <= n; ++i) {
      double x, y;
      scanf("%lf%lf", &x, &y);
      d[i] = dist(x0, y0, x, y);
    }
    sort(d + 1, d + n + 1);
    double l = 0, r = d[n] + 1;
    double ans = cal(l, r);
    printf("%.15lf\n", ans);
  }
  return 0;
}
