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

#define SZ(a) (int)a.size()
#define ALL(a) a.begin(), a.end()
#define FOR(i, a, b) for (int i = (a); i<(b); ++i)
#define RFOR(i, b, a) for (int i = (b)-1; i>=(a); --i)
#define MP make_pair
#define PB push_back
#define F first
#define S second

typedef long long LL;
typedef pair<int, int> PII;
typedef vector<int> VI;

int main()
{
	ios::sync_with_stdio(false);
	cin.tie(0);
	int n, k;
	cin >> n >> k;
	double ans = 0;
	vector<double> p(n);
	FOR (i, 0, n) cin >> p[i];
	sort(ALL(p), greater());
	vector<vector<double>> dp(n + 1, vector<double>(2 * n + 1, 0));
	dp[0][n] = 1;
	double cur = 0;
	FOR (i, 0, n)
	{
		cur = 0;
		FOR (j, -i, i + 1)
		{
			if (j >= k) cur += dp[i][n + j];
			dp[i + 1][n + j + 1] += dp[i][n + j] * p[i];
			dp[i + 1][n + j - 1] += dp[i][n + j] * (1 - p[i]);
		}
		ans = max(ans, cur);
	}
	cur = 0; 
	FOR (i, k, n + 1) cur += dp[n][n + i];
	ans = max(ans, cur);
	cout << ans << '\n';
	
	
	return 0;
}