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#include<bits/stdc++.h>
using namespace std;
//mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());
#define mod 998244353
#define ll long long
#define inf 0x3f3f3f3f
#define INF 0x3f3f3f3f3f3f3f3f
inline int read()
{
	char ch=getchar(); int nega=1; while(!isdigit(ch)) {if(ch=='-') nega=-1; ch=getchar();}
	int ans=0; while(isdigit(ch)) {ans=ans*10+ch-48;ch=getchar();}
	if(nega==-1) return -ans;
	return ans;
}
void print(vector<int> x){for(int i=0;i<(int)x.size();i++) printf("%d%c",x[i]," \n"[i==(int)x.size()-1]);}
#define N 50005
using db=long double;
const db eps=1e-13;
db a[N],f[N],g[N];
int n,t;
signed main()
{
	cin>>n>>t;
	for(int i=1;i<=n;i++) scanf("%Lf",&a[i]);
	f[0]=1; int l=0,r=0;
	sort(a+1,a+n+1,greater());
	db ans=0;
	for(int i=1;i<=n;i++)
	{
		for(int j=l;j<=r+1;j++) g[j]=0;
		for(int j=l;j<=r;j++) g[j]+=f[j]*(1-a[i]),g[j+1]+=f[j]*a[i];
		for(int j=l;j<=r+1;j++) f[j]=g[j];
		// printf("%d %d : ",l,r);
		// for(int j=l;j<=r;j++) printf("%.2Lf ",f[j]);
		// cout<<"\n";
		db res=0;
		for(int j=l;j<=r+1;j++) if(j-(i-j)>=t) res+=f[j];
		ans=max(ans,res);
		while(f[l]<eps) l++;
		r++;
		while(f[r]<eps) r--;
	}
	printf("%.10Lf\n",ans);
	return 0;
}