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

using ll=int64_t;
#define int ll

#define FOR(i,a,b) for(int i=int(a);i<int(b);i++)
#define REP(i,b) FOR(i,0,b)
#define MP make_pair
#define PB push_back
#define ALL(x) x.begin(),x.end()
#define REACH cerr<<"reached line "<<__LINE__<<endl
#define DMP(x) cerr<<"line "<<__LINE__<<" "<<#x<<":"<<x<<endl
#define ZERO(x) memset(x,0,sizeof(x))

using pi=pair<int,int>;
using vi=vector<int>;
using ld=long double;

template<class T,class U>
ostream& operator<<(ostream& os,const pair<T,U>& p){
	os<<"("<<p.first<<","<<p.second<<")";
	return os;
}

template<class T>
ostream& operator <<(ostream& os,const vector<T>& v){
	os<<"[";
	REP(i,(int)v.size()){
		if(i)os<<",";
		os<<v[i];
	}
	os<<"]";
	return os;
}

int read(){
	int i;
	scanf("%" SCNd64,&i);
	return i;
}

void printSpace(){
	printf(" ");
}

void printEoln(){
	printf("\n");
}

void print(int x,int suc=1){
	printf("%" PRId64,x);
	if(suc==1)
		printEoln();
	if(suc==2)
		printSpace();
}

string readString(){
	static char buf[3341000];
	scanf("%s",buf);
	return string(buf);
}

char* readCharArray(){
	static char buf[3341000];
	static int bufUsed=0;
	char* ret=buf+bufUsed;
	scanf("%s",ret);
	bufUsed+=strlen(ret)+1;
	return ret;
}

template<class T,class U>
void chmax(T& a,U b){
	if(a<b)
		a=b;
}

template<class T,class U>
void chmin(T& a,U b){
	if(a>b)
		a=b;
}

template<class T>
T Sq(const T& t){
	return t*t;
}

const int inf=LLONG_MAX/3;

ld pou(ld x,int a){
	ld res=1;
	REP(i,a)res*=x;
	return res;
}

const int Nmax=20;
int binom[Nmax][Nmax];
void Init(){
	binom[0][0]=1;
	REP(i,Nmax)REP(j,Nmax){
		if(i-1>=0)binom[i][j]+=binom[i-1][j];
		if(j-1>=0)binom[i][j]+=binom[i][j-1];
	}
}
int Choose(int a,int b){
	return binom[a-b][b];
}

map<pi,ld> mult(map<pi,ld>a,map<pi,ld>b){
	map<pi,ld> res;
	for(auto kv1:a)for(auto kv2:b){
		int t=kv1.first.first+kv2.first.first;
		int x=kv1.first.second+kv2.first.second;
		res[pi(t,x)]+=kv1.second*kv2.second;
	}
	return res;
}

map<pi,ld> rev(map<pi,ld>a){
	map<pi,ld>res;
	for(auto kv:a)
		res[pi(kv.first.second,kv.first.first)]=kv.second;
	return res;
}

map<pi,ld> integrate(map<pi,ld>a,ld b,ld c){
	map<pi,ld>res;
	for(auto kv:a){
		int t=kv.first.first,x=kv.first.second;
		REP(i,t+2){
			if(i%2==0){
				res[pi(0,t+1-i+x)]+=kv.second/(t+1)*pou(c,i)*Choose(t+1,i);
			}else{
				res[pi(0,t+1-i+x)]-=kv.second/(t+1)*pou(c,i)*Choose(t+1,i);
			}
		}
		res[pi(0,x)]-=kv.second/(t+1)*pou(b,t+1);
	}
	return res;
}

ld solve(const vector<ld>&use,const vector<ld>&rem,const vi&idx){
	//cerr<<use<<" "<<rem<<" "<<idx<<endl;
	map<pi,ld> f;
	f[pi(0,0)]=1;
	ld b=use[0];
	int n=use.size(),m=rem.size();
	REP(i,m)if(idx[i]==0){
		map<pi,ld>g;
		g[pi(0,0)]=-rem[i];
		g[pi(0,1)]=1;
		f=mult(f,g);
		chmax(b,rem[i]);
	}
	FOR(i,1,n){
		ld w=use[i];
		f=rev(f);
		REP(j,m)if(idx[j]==i){
			map<pi,ld>g;
			g[pi(0,0)]=-rem[j];
			g[pi(0,1)]=1;
			g[pi(1,0)]=-1;
			f=mult(f,g);
			chmax(w,rem[j]);
		}
		f=integrate(f,b,w);
		b+=w;
	}
	ld ans=0;
	if(b<1)
		for(auto kv:f)
			ans+=kv.second;
	//cerr<<ans<<endl;
	return ans;
}

ld sub(const vector<ld>&use,const vector<ld>&rem,int i,vi&idx){
	if(i==int(rem.size()))
		return solve(use,rem,idx);
	ld ans=0;
	REP(j,use.size()){
		idx[i]=j;
		ans+=sub(use,rem,i+1,idx);
	}
	return ans;
}

ld calc(const vector<ld>&use,const vector<ld>&rem){
	int n=use.size();
	vi perm(n);REP(i,n)perm[i]=i;
	ld res=0;
	do{
		vector<ld> tmp(use.size());
		REP(i,use.size())tmp[i]=use[perm[i]];
		vi idx(rem.size());
		res+=sub(tmp,rem,0,idx);
	}while(next_permutation(perm.begin()+1,perm.end()));
	return res;
}

signed main(){
	Init();
	int n=read(),c=read();
	vector<ld> l(n);
	REP(i,n){
		l[i]=read();
		l[i]/=c;
	}
	ld ans=0;
	FOR(bit,1,1<<n){
		vector<ld> use,rem;
		REP(i,n)
			if((bit>>i)&1)
				use.PB(l[i]);
			else
				rem.PB(l[i]);
		ld w=calc(use,rem);
		if(int(use.size())%2==1)
			ans+=w;
		else
			ans-=w;
	}
	cout<<fixed<<setprecision(20)<<1.0-ans<<endl;
}