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

using namespace std;

bool comp (long double a, long double b) {
  return a > b;
}

int main() {
	
	int n, t;
	cin >> n >> t;
	vector<long double> probs(n);
	for (int i = 0; i < n; i++) {
		long double x;
		cin >> x;
		probs[i] = x;
	}
	sort(probs.begin(), probs.end(), comp);
	
	vector<long double> even_pts_pr(2 * n + 1, 0.0L);
	vector<long double> odd_pts_pr(2 * n + 1, 0.0L);
	int initial_points = n;
	int required_points = n + t;
	
	even_pts_pr[n] = 1.0L;
	
	long double max_prob = 0.0L;

	for (int i = 0; i < n; i++) {
		long double prob = 0.0L;
		if (i % 2 == 0) {
			for (int j = n - i - 1; j <= n + i + 1; j += 2) {
				odd_pts_pr[j] = even_pts_pr[j - 1] * probs[i] + even_pts_pr[j + 1] - even_pts_pr[j+1] * probs[i];
				if (j >= required_points) {
					prob += odd_pts_pr[j];
				}
			}
		} else if (i % 2 == 1) {
			for (int j = n - i - 1; j <= n + i + 1; j += 2) {
				even_pts_pr[j] = odd_pts_pr[j - 1] * probs[i] + odd_pts_pr[j + 1] - odd_pts_pr[j+1] * probs[i];
				if (j >= required_points) {
					prob += even_pts_pr[j];
				}
			}
		}
		
		if (prob > max_prob) {
			max_prob = prob;
		}
	}
	
	cout << setprecision(10) << max_prob;
	
}