#include <bits/stdc++.h>
using namespace std;
int N, K, ep, xo, yo, x[200], y[200];
double d[200];
double f[200];
double dp[200][200];
double p(double r) {
  for (int i = 0; i < (int)(N); i++) {
    if (d[i] < r)
      f[i] = 1;
    else
      f[i] = exp(1 - d[i] * d[i] / (r * r));
  }
  for (int i = 0; i < (int)(N + 1); i++)
    for (int j = 0; j < (int)(N + 1); j++) dp[i][j] = 0;
  dp[0][0] = 1;
  for (int i = 0; i < (int)(N); i++)
    for (int j = 0; j < (int)(N + 1); j++) {
      dp[i + 1][j + 1] += dp[i][j] * f[i];
      dp[i + 1][j] += dp[i][j] * (1 - f[i]);
    }
  double s = 0;
  for (int i = 0; i < (int)(K); i++) s += dp[N][i];
  return s;
}
int main() {
  cin >> N >> K >> ep >> xo >> yo;
  for (int i = 0; i < (int)(N); i++) cin >> x[i] >> y[i];
  for (int i = 0; i < (int)(N); i++)
    d[i] = hypot((double)x[i] - xo, (double)y[i] - yo);
  double l = 0, r = 1e9, m;
  for (int q = 0; q < (int)(100); q++) {
    m = (l + r) / 2;
    if (p(m) * 1000 < ep)
      r = m;
    else
      l = m;
  }
  printf("%.8f\n", l);
  return 0;
}
