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#include <bits/stdc++.h>
using namespace std;
const double PI=acos(-1);
using cd=complex<double>;
/*void fft(vector<cd>&a,bool inv)
{
	int n=a.size();
	if(n==1)
		return;
	vector<cd>a0(n/2),a1(n/2);
	for(int i=0; i*2<n; i++)
		a0[i]=a[i*2],a1[i]=a[2*i+1];
	fft(a0,inv);
	fft(a1,inv);
	double ang=2*PI/n*(inv?-1:1);
	cd w(1),wn(cos(ang),sin(ang));
	for(int i=0; i*2<n; i++)
	{
		a[i]=a0[i]+w*a1[i];
		a[i+n/2]=a0[i]-w*a1[i];
		if(inv)
			a[i]/=2,a[i+n/2]/=2;
		w*=wn;
	}
}*/
using LL=long long;//                                                               fft oraz header chamsko zajebane z https://github.com/tonowak/acmlib/blob/master/code/math/fft/main.cpp
#define FOR(i,l,r)for(int i=(l);i<=(r);++i)
#define REP(i,n)FOR(i,0,(n)-1)
#define ssize(x)int(x.size())
#ifdef DEBUG
auto&operator<<(auto&o,pair<auto,auto>p){return o<<"("<<p.first<<", "<<p.second<<")";}
auto operator<<(auto&o,auto x)->decltype(x.end(),o){o<<"{";int i=0;for(auto e:x)o<<","+!i++<<e;return o<<"}";}
#define debug(X...)cerr<<"["#X"]: ",[](auto...$){((cerr<<$<<"; "),...)<<endl;}(X)
#else
#define debug(...){}
#endif
void fft(vector<cd> &a) {
	int n = ssize(a), L = 31 - __builtin_clz(n);
	static vector<complex<long double>> R(2, 1);
	static vector<cd> rt(2, 1);
	for(static int k = 2; k < n; k *= 2) {
		R.resize(n), rt.resize(n);
		auto x = polar(1.0L, acosl(-1) / k);
		FOR(i, k, 2 * k - 1)
			rt[i] = R[i] = i & 1 ? R[i / 2] * x : R[i / 2];
	}
	vector<int> rev(n);
	REP(i, n) rev[i] = (rev[i / 2] | (i & 1) << L) / 2;
	REP(i, n) if(i < rev[i]) swap(a[i], a[rev[i]]);
	for(int k = 1; k < n; k *= 2) {
		for(int i = 0; i < n; i += 2 * k) REP(j, k) {
			cd z = rt[j + k] * a[i + j + k]; // mozna zoptowac rozpisujac
			a[i + j + k] = a[i + j] - z;
			a[i + j] += z;
		}
	}
} // END HASH
vector<double> conv(vector<double> &a, vector<double> &b) {
	if(a.empty() || b.empty()) return {};
	vector<double> res(ssize(a) + ssize(b) - 1);
	int L = 32 - __builtin_clz(ssize(res)), n = (1 << L);
	vector<cd> in(n), out(n);
	copy(a.begin(), a.end(), in.begin());
	REP(i, ssize(b)) in[i].imag(b[i]);
	fft(in);
	for(auto &x : in) x *= x;
	REP(i, n) out[i] = in[-i & (n - 1)] - conj(in[i]);
	fft(out);
	REP(i, ssize(res)) res[i] = imag(out[i]) / (4 * n);
	return res;
}
/*vector<double>mult(vector<double>a,vector<double>b)
{
	//cout<<"hmmm\n";
	int n1=1;
	while(n1<a.size()+b.size()-1)
		n1<<=1;
	vector<cd>v1(n1,0.0),v2(n1,0.0);
	for(int i=0; i<a.size(); i++)
		v1[i]=(a[i]);
	for(int i=0; i<b.size(); i++)
		v2[i]=(b[i]);
	//cout<<"sus1\n";
	//cout<<v1[0].real()<<" "<<v1[2].real()<<"suuuuuu\n";
	//cout<<v2[0].real()<<" "<<v2[2].real()<<"suuuuuus\n";
	fft(v1,0);
	fft(v2,0);
	//cout<<"sus2\n";
	for(int i=0; i<n1; i++)
		v1[i]=v1[i]*v2[i];
	fft(v1,1);
	//cout<<"sus3\n";
	vector<double>res(n1);
	for(int i=0; i<n1; i++)
		res[i]=v1[i].real();
	return res;
}*/
	//vector<int>powe2={1,2,4,8,16,32,64,128,256,512,1024,2048,4096,8192,16384,32768,65536,131072,262144,524288};
	vector<vector<double>>tree;
	int k,t,murzyn;
double poly(int il)
{
	il++;
	//cout<<il<<"kurwidolek\n";
	int sm=0;
	vector<double>res={1.0};
	int pt=k+1;
	pt/=2;
	int pom=1;
	vector<int>sus;
	while(sm!=il)
	{
		if(sm+pt<=il)
		{
			//res=conv(res,tree[pom*2]);
			sus.push_back(pom*2);
			pom=pom*2+1;
			sm+=pt;
		}
		else
			pom*=2;
		pt/=2;
	}
	for(int i=sus.size()-1; i>=0; i--)
		res=conv(res,tree[sus[i]]);
	double res1=0.0;
	//for(int i=0; i<res.size(); i++)
	//	printf("%.7f ",res[i]);
	//cout<<"\n";
	vector<double>guwno;
	for(int i=res.size()-1; i*2>=t+il; i--)
		guwno.push_back(res[i]);
	int sex=1;
	while(sex<guwno.size())
	{
	for(int i=0; i+sex<guwno.size(); i+=sex*2)
		guwno[i]+=guwno[i+sex];
	sex*=2;
	}
	if(guwno.size())
		res1=guwno[0];
	//res1+=res[i];
	return res1;
}
int main()
{
	int n;
	scanf("%d%d", &n, &t);
	vector<double>v(n),vp(n,1.0);
	for(int i=0; i<n; i++)
		scanf("%lf", &v[i]);
	sort(v.begin(),v.end());
	reverse(v.begin(),v.end());
	for(int i=0; i<n; i++)
		vp[i]-=v[i];
	k=1;
	murzyn=1;
	while(k<=n)
		k*=2,murzyn++;
	k--;
	tree.resize(k*2+2);
	for(int i=n+k+1; i<k*2+2; i++)
		tree[i]={1.0};
	for(int i=0; i<n; i++)
		tree[i+k+1]={vp[i],v[i]};
	//cout<<n<<"wieeeeellllkaaaa\n";
	for(int i=k; i>0; i--)
			tree[i]=conv(tree[i*2],tree[2*i+1]);
	//cout<<"duuuuupaaaaa------------------------\n";
	int p=0,kon=n/2;
	/*cout<<"pen%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%\n";
	for(int i=0; i<n; i++)
	{
		cout<<i+1<<". ";
		printf("%.7f\n",poly(i));
	}
	cout<<"pen%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%\n";*/
	//cout<<"penis\n";
	//return 0;
	
	while(kon-p>1)
	{
		int chuj=kon-p+1;
		chuj/=3;
		double r1=poly((p+chuj-1)*2),r2=poly((kon-chuj+1)*2);
		if(r1<r2)
			p+=chuj;
		else
			kon-=chuj;
	}	
	double wyn=0.0;
	if(0<=p*2&&p*2<n)
		wyn=max(wyn,poly(p*2));
	if(0<=kon*2&&kon*2<n)
		wyn=max(wyn,poly(kon*2));
	/*for(int i=p-100; i<=kon+100; i++)
		if(0<=i*2&&i*2<n)
		{
			//if(poly(i*2-2)>poly(i*2)&&poly(i*2)<poly(i*2+2))
			//	{cout<<"kurwaaaaa\n";return 0;}
			wyn=max(wyn,poly(i*2));
		}*/
		p=0,kon=n/2;
	while(kon-p>1)
	{
		int chuj=kon-p+1;
		chuj/=3;
		double r1=poly((p+chuj-1)*2+1),r2=poly((kon-chuj+1)*2+1);
		if(r1<r2)
			p+=chuj;
		else
			kon-=chuj;
	}
	if(0<=p*2+1&&p*2+1<n)
		wyn=max(wyn,poly(p*2+1));
	if(0<=kon*2+1&&kon*2+1<n)
		wyn=max(wyn,poly(kon*2+1));
	/*for(int i=p-100; i<=kon+100; i++)
			if(0<=i*2+1&&i*2+1<n)
		{
			//if(poly(i*2-1)>poly(i*2+1)&&poly(i*2+1)<poly(i*2+3))
			//	{cout<<"kurwaaaaa\n";return 0;}
			wyn=max(wyn,poly(i*2+1));
		}*/
	//cout<<"co kurwa???\n";
	printf("%.7lf\n",wyn);
}