//2019.11.13 by ljz
//#pragma GCC optimize(2)
//email 573902690@qq.com
//if you find any bug in my code
//please tell me
#include<bits/stdc++.h>
//#include<ext/pb_ds/tree_policy.hpp>
//#include<ext/pb_ds/assoc_container.hpp>
using namespace std;
//using namespace __gnu_pbds;
//using namespace __gnu_cxx;
#define res register int
#define LL long long
#define inf 0x3f3f3f3f
#define INF 0x3f3f3f3f3f3f3f
#define unl __int128
#define eps 1e-9
#define RG register
#define db double
//#define pc(x) __builtin_popcount(x)
#define ctz(x) __builtin_ctz(x)
#define pc(x) __builtin_popcountll(x)
typedef pair<int,int> Pair;
#define mp make_pair
#define fi first
#define se second
#define pi acos(-1.0)
#define pb push_back
#define ull unsigned LL
#define lowbit(x) (x&-x)
#define gc getchar
//template <class T>using Tree=tree<T,null_type,less<T>,rb_tree_tag,tree_order_statistics_node_update>;
//inline char gc() {
//    static char buf[100000],*p1,*p2;
//    return p1==p2&&(p2=(p1=buf)+fread(buf,1,100000,stdin),p1==p2)?EOF:*p1++;
//}
//inline int read() {
//    res s=0,ch=gc();
//    while(ch<'0'||ch>'9')ch=gc();
//    while(ch>='0'&&ch<='9')s=s*10+ch-'0',ch=gc();
//    return s;
//}
//char sr[1<<21],z[20];
//int C=-1,Z=0;
//inline void Ot(){fwrite(sr,1,C+1,stdout),C=-1;}
//inline void print(res x){
//    if(C>1<<20)Ot();if(x<0)sr[++C]='-',x=-x;
//    while(z[++Z]=x%10+48,x/=10);
//    while(sr[++C]=z[Z],--Z);sr[++C]='\n';
//}
inline int read() {
    res s=0,ch=gc(),w=1;
    while(ch<'0'||ch>'9'){if(ch=='-')w=-1;ch=gc();}
    while(ch>='0'&&ch<='9')s=s*10+ch-'0',ch=gc();
    return s*w;
}
inline LL Read() {
    RG LL s=0;
    res ch=gc();
    while(ch<'0'||ch>'9')ch=gc();
    while(ch>='0'&&ch<='9')s=s*10+ch-'0',ch=gc();
    return s;
}
//inline LL Read() {
//    RG LL s=0;
//    res ch=gc(),w=1;
//    while(ch<'0'||ch>'9'){if(ch=='-')w=-1;ch=gc();}
//    while(ch>='0'&&ch<='9')s=s*10+ch-'0',ch=gc();
//    return s*w;
//}
//inline void write(RG unl x){
//    if(x>10)write(x/10);
//    putchar(int(x%10)+'0');
//}
inline void swap(res &x,res &y) {
    x^=y^=x^=y;
}
//mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
//clock_t start=clock();
//inline void ck(){
//    if(1.0*(clock()-start)/CLOCKS_PER_SEC>0.1)exit(0);
//}
const int kcz=1000000009;
inline void add(res &x,const res &y){
    x+=y,x>=kcz?x-=kcz:(x<0?x+=kcz:1);
}
inline int Add(const res &x,const res &y){
    return x+y>=kcz?x+y-kcz:(x+y<0?x+y+kcz:x+y);
}
inline int mul(const res &x,const res &y){
    return int(1LL*x*y%kcz);
}
inline int mul(const res &x,const res &y,const res &d){
    return int(1LL*x*y/d%kcz);
}
inline int sqr(const res &x){
    return int(1LL*x*x%kcz);
}
inline int qpow(res x,res y){
    res ret=1;
    while(y){
        if(y&1)ret=mul(ret,x);
        x=mul(x,x),y>>=1;
    }
    return ret;
}
inline LL Qpow(RG LL x,res y){
    RG LL ret=1;
    while(y){
        if(y&1)ret*=x;
        x*=x,y>>=1;
    }
    return ret;
}
namespace MAIN{
    int n,c;
    LL dp[1<<5][1<<5][300+10];
    int a[6];
    inline void MAIN(){
        n=read(),c=read(),c*=n;
        for(res i=0;i<n;i++)a[i]=read()*n;
        sort(a,a+n),dp[0][0][a[n-1]]=1;
        res end=(1<<(n-1))-1;
        for(res x=1;x<c;x++)
            if(x%n){
                for(res l=x+1;l<=c;l++)for(res S=0;S<=end;S++){
                        res qaq=1<<(x%n-1);
                        if(S&qaq)continue;
                        for(res nS=0;nS<=end;nS++){
                            if(!dp[S][nS][l])continue;
                            RG LL r=dp[S][nS][l];
                            for(res y=0;y<n-1;y++){
                                if(nS&(1<<y))continue;
                                dp[S|qaq][nS|1<<y][min(c,max(x+a[y],l))]+=r;
//                                printf("%lld\n",r);
                            }
                        }
                    }
            }
//        printf("%lld\n",dp[end][end][c]);
        RG LL ret=1;
        RG db ans=dp[end][end][c];
        c/=n;
        for(res i=1;i<n;i++)ret*=i*c;
//        ret*=c;
//        printf("%lld\n",ret);
        printf("%.15lf\n",ans/ret);
    }
}
int main(){
//    freopen("money.in","r",stdin);
//    freopen("money.out","w",stdout);
//    srand(19260817);
    MAIN::MAIN();
//    Ot();
    return 0;
}

Measured memory_bytes: 1408