#include<bits/stdc++.h>
using namespace std;
using ll = long long;
ll n;
ll k;

int main()
{
	cin>>n>>k;
	//f[i][j]:Ñ¡ÔñµÄ´ðÇ°i¸öÌâÄ¿£¬×îÖյ÷ÖΪjµÄ¸ÅÂÊ 
	vector<vector<double>> f(2 * n + 10,vector<double>(2 * n + 10));
	ll bas = n + 1;
	vector<double> a(n + 1);
	for(int i = 1;i<=n;i++)
	{
		cin>>a[i];
	}
	sort(a.begin()+1,a.end());
	reverse(a.begin()+1,a.end());
	//Ò»ÌⲻѡµÄÄÃ0·ÖµÄ¸ÅÂÊÊÇ1 
	f[0][bas] = 1;
	double ans = 0;
	//×ö¶Ô¸ÅÂÊ×î´óµÄkÌâÈ«²¿¶ÔµÄ¸ÅÂʾÍÊÇ×î´ó¼°¸ñ¸ÅÂÊ 
	// ps:×¢ÒâÕâÀï´ð´íÁËÒª¼õ·ÖµÄ 
	for(int i = 1;i <= n;i++)
	{
		ll l = bas - i;
		ll r = bas + i;
		//´ÓÈ«´íµ½È«¶Ô 
		for(int j = l;j <= r;j++)
		{
			f[i][j] = f[i-1][j-1] * a[i] + f[i-1][j+1] * (1.0 - a[i]);
//			cout<<f[i][j]<<endl;
//			cout<<i<<' '<<j<<endl;
		}
		double res = 0;
		for(int j = k + bas;j<=r;j++)
		{
			res += f[i][j];
		}
//		cout<<res<<endl;
		ans = max(ans,res);
	}
//	for(int i = 1;i<=n;i++)
//	{
//		for(int j = k;j<=i;j++)
//		{
//			ans += f[i][j];
//		}
//	}
	cout<<ans<<endl;
	return 0;
}