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#include <iostream>
#include <vector>
#include <array>
#include <algorithm>
#include <iomanip> 
#include <cmath>

using namespace std;

int main()
{
    int n;
    int t;
    cin >> n >> t;

	vector<double> prob;

	for (int i = 0; i < n; i++)
	{
		double x;
		cin >> x;
		prob.push_back(x);
	}

	sort(prob.begin(), prob.end());

	vector<double> total;
	for (int i = 0; i < n; i++)
	{
		total.push_back(0);
	}

	int items = 1 << n;

	for (int i = 0; i < items; i++)
	{
		vector <short> temp;
		for (int j = 0; j < n; j++) {
			short bit = (i >> (n - j - 1)) & 1;
			temp.push_back(bit);
		}

		for (int ver = 0; ver < n - 1; ver++) {
			int wynik = 0;
			for (int j = ver; j < n; j++) {
				wynik += (temp[j] == 1) ? 1 : -1;
			}
			if (wynik >= t) {
				double p = 1;
				for (int j = 0; j < n; j++) {
					p *= (temp[j] == 1) ? prob[j] : (1 - prob[j]);
				}
				total[ver] += p;
			}
		}

	}

	auto it = max_element(total.begin(), total.end());
	double wynik = *it;
	wynik = round(wynik * 100000000) / 100000000;

	cout << setprecision(7) << wynik << endl;
}