#include <bits/stdc++.h>
using namespace std;
const int MaxN = 102, MaxL = 10004, MaxC = 0x3F3F3F3F, NA = -1;
int x[MaxN], y[MaxN];
double d[MaxN];
double p[MaxN];
double f[MaxN][MaxN];
int k, n;
double eps;
int main(void) {
  int i, j, l, x0, y0;
  double cur, lo, me, hi, r2;
  while (scanf(" %d", &n) != EOF) {
    scanf(" %d %d", &k, &i);
    eps = i / 1000.0;
    eps = 1.0 - eps;
    scanf(" %d %d", &x0, &y0);
    for (i = 0; i < n; i++) {
      scanf(" %d %d", &x[i], &y[i]);
      x[i] -= x0;
      y[i] -= y0;
      d[i] = x[i] * x[i] + y[i] * y[i];
    }
    lo = 0.0;
    hi = MaxL;
    for (j = 0; j < 100; j++) {
      me = (lo + hi) * 0.5;
      r2 = me * me;
      for (i = 0; i < n; i++)
        if (d[i] <= r2)
          p[i] = 1.0;
        else
          p[i] = exp(1.0 - d[i] / r2);
      memset(f, 0, sizeof(f));
      f[0][0] = 1.0;
      for (i = 0; i < n; i++)
        for (l = 0; l <= n; l++) {
          f[i + 1][l] += f[i][l] * (1.0 - p[i]);
          f[i + 1][l + 1] += f[i][l] * p[i];
        }
      cur = 0;
      for (l = k; l <= n; l++) cur += f[n][l];
      if (cur < eps)
        lo = me;
      else
        hi = me;
    }
    printf("%.15lf\n", (double)lo);
  }
  return 0;
}
