#include <bits/stdc++.h>
using namespace std;
struct _ {
  _() { ios_base::sync_with_stdio(0); }
} _;
template <class A, class B>
ostream &operator<<(ostream &o, pair<A, B> t) {
  o << "(" << t.first << ", " << t.second << ")";
  return o;
}
template <class T>
string tostring(T first, int len = 0, char c = '0') {
  stringstream ss;
  ss << first;
  string r = ss.str();
  if (r.length() < len) r = string(len - r.length(), c) + r;
  return r;
}
template <class T>
void PV(T a, T b, int n = 0, int w = 0, string s = " ") {
  int c = 0;
  while (a != b) {
    cout << tostring(*a++, w, ' ');
    if (a != b && (n == 0 || ++c % n))
      cout << s;
    else
      cout << endl;
  }
}
template <class T>
inline bool chmin(T &a, T b) {
  return a > b ? a = b, 1 : 0;
}
template <class T>
inline bool chmax(T &a, T b) {
  return a < b ? a = b, 1 : 0;
}
const long long linf = 0x3f3f3f3f3f3f3f3fLL;
const int inf = 0x3f3f3f3f;
const int mod = int(1e9) + 7;
const int N = 111;
const double eps = 1e-10;
const double e = 2.7182818284590452353602874713527;
double getP(double D, double R) {
  if (D <= R + 1e-10)
    return 1;
  else
    return pow(e, (1 - D * D / R / R));
}
double dist2(double x0, double y0, double x1, double y1) {
  return sqrt((x0 - x1) * (x0 - x1) + (y0 - y1) * (y0 - y1));
}
double d[N];
int enemy;
int target;
double ee;
double X0, Y0;
double dp[N][N];
double possibility(double *p, int n, int K) {
  memset(dp, 0, sizeof(dp));
  ;
  dp[0][0] = 1;
  for (int i = 0; i < n; i++)
    for (int k = 0; k <= i; k++) {
      dp[i + 1][k] += (1 - p[i]) * dp[i][k];
      dp[i + 1][k + 1] += (p[i]) * dp[i][k];
    }
  double res = 0;
  for (int k = 0; k < K; k++) res += dp[n][k];
  return res;
}
int main() {
  cin >> enemy >> target >> ee;
  cin >> X0 >> Y0;
  for (int i = 0; i < enemy; i++) {
    double first, second;
    cin >> first >> second;
    d[i] = dist2(X0, Y0, first, second);
  }
  double L = 0, R = 5000;
  for (int iter = 0; iter < 100; iter++) {
    double M = (L + R) / 2;
    double p[N] = {};
    for (int j = 0; j < enemy; j++) p[j] = getP(d[j], M);
    double pp = possibility(p, enemy, target);
    if (1000 * pp > ee) {
      L = M;
    } else {
      R = M;
    }
  }
  cout << fixed << setprecision(12) << L << endl;
  return 0;
}
