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#include <cstdio>
#include <vector>
#include <algorithm>

using namespace std;

int main() {
  int n, t; scanf("%d %d", &n, &t);
  int N = n+3;
  vector<double> p(n); for (int i=0; i<n; ++i) scanf(" %lf", &p[i]);
  vector<double> s(N, 1.); s[0] = 0.; 

  double res = 0.; 

  sort(p.begin(), p.end(), greater<double>());

  for (int i=0; i<n; ++i)  { 
    double pp = p[i];
 
    double prev = 0.;
    for (int j=0; j<=i; ++j) {
      double tmp = s[j+1];
      s[j+1] = prev * pp + tmp * (1. - pp);
      prev = tmp;
    }
/*
    for (int j=0; j<=i+1; ++j) {
      printf("%.2lf ", s[j]);
    }
    printf("\n");
*/
    res = max(res, 1.-s[(t+i+2)/2]);
  }

  printf("%.7lf\n", res);
  return 0;
}