#include <bits/stdc++.h>
using namespace std;
using namespace std;
long long powm(long long base, long long exp, long long mod = 1000000007) {
  long long ans = 1;
  while (exp) {
    if (exp & 1) ans = (ans * base) % mod;
    exp >>= 1, base = (base * base) % mod;
  }
  return ans;
}
long long x[105], y[105], n, k;
long double epsilon;
long double dp[105][105];
long double p(long long a, long long b, long double radius) {
  if ((a - x[0]) * (a - x[0]) + (b - y[0]) * (b - y[0]) <= radius * radius)
    return 1;
  else
    return exp(1 - (((a - x[0]) * (a - x[0]) + (b - y[0]) * (b - y[0])) /
                    (radius * radius)));
}
bool check(long double mid) {
  for (long long i = 0; i < n + 1; i++)
    for (long long j = 0; j < n + 1; j++) dp[i][j] = 0;
  dp[0][0] = 1;
  for (long long i = 1; i < n + 1; i++)
    for (long long j = 0; j < n + 1; j++)
      dp[i][j] = dp[i - 1][j] * (1 - p(x[i], y[i], mid)) +
                 dp[i - 1][j - 1] * (p(x[i], y[i], mid));
  long double tmp = 0;
  for (long long i = k; i < n + 1; i++) tmp += dp[n][i];
  return (tmp >= (1 - epsilon));
}
int main() {
  cin >> n >> k >> epsilon;
  epsilon /= 1000;
  for (long long i = 0; i < n + 1; i++) cin >> x[i] >> y[i];
  long double low = 0, high = 10000, mid;
  for (long long iter = 0; iter < 500; iter++) {
    mid = (low + high) / 2;
    if (check(mid))
      high = mid;
    else
      low = mid;
  }
  cout << fixed << setprecision(10) << low;
  return 0;
}
