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#include <bits/stdc++.h>
using namespace std;

long double dp[100007][2];

int main() 
{
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	int n, t;
	long double x, wyn = 0.0, tempwyn;
	cin >> n  >> t;
	vector<long double> pr;
	for(int i = 0; i < n; i++)
	{
		cin >> x;
		pr.push_back(x);
	}
	sort(pr.begin(), pr.end());
	reverse(pr.begin(), pr.end());
	dp[50002][0] = 1.0;
	for(int i = 1; i <= n; i++)
	{
		tempwyn = 0.0;
		for(int j = n; j >= -n; j--)
		{
			dp[50002 + j][i % 2] = pr[i - 1] * dp[50002 + j - 1][(i + 1) % 2] + (1.0 - pr[i - 1]) * dp[50002 + j + 1][(i + 1) % 2];
			//cout << i << " " << j << " " << dp[i][j] << endl;
		}
		for(int j = t; j <= n; j++)
		{
			tempwyn += dp[50002 + j][i % 2];
		}
		wyn = max(wyn, tempwyn);
	}
	cout << fixed << setprecision(10) << wyn << endl;
	return 0;
}