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

#define int long long

#define rep(i,n) for(int i=0;i<(n);i++)
#define pb push_back
#define all(v) (v).begin(),(v).end()
#define fi first
#define se second
typedef vector<int>vint;
typedef pair<int,int>pint;
typedef vector<pint>vpint;

template<typename A,typename B>inline void chmin(A &a,B b){if(a>b)a=b;}
template<typename A,typename B>inline void chmax(A &a,B b){if(a<b)a=b;}

typedef double D;

int C,X;
int dp[1<<5][55][55][6];
int calc(vint L){
    int N=L.size();
    memset(dp,0,sizeof(dp));
    dp[0][0][X-1][N]=1;
    for(int i=0;i<1<<N;i++){
        for(int j=0;j<C;j++){
            for(int k=0;k<=C;k++){
                for(int l=0;l<=N;l++){
                    if(dp[i][j][k][l]==0)continue;
                    int sup=(1<<N)-1-i;
                    int sub=sup;
                    do{
                        bool ok=true;
                        if(j==k)ok&=(((1<<l)-1)&sub)!=0;
                        if(ok){
                            pint ma(k,l);
                            rep(s,N)if(sub>>s&1)chmax(ma,pint(min(j+L[s],C),s));
                            dp[i|sub][j+1][ma.fi][ma.se]+=dp[i][j][k][l];
                        }
                        sub=(sub-1)&sup;
                    }while(sup!=sub);
                }
            }
        }
    }
    int ans=0;
    rep(i,N)ans+=dp[(1<<N)-1][C][C][i];
    return ans;
}

signed main(){
    int N;
    cin>>N>>C;
    vint L(N);rep(i,N)cin>>L[i];
    sort(all(L));
    X=L.back();

    vint p(N-1);
    rep(i,N-1)p[i]=i;

    int ei=0;
    do{
        vint l(N-1);
        rep(i,N-1)l[i]=L[p[i]];
        ei+=calc(l);
    }while(next_permutation(all(p)));

    D ans=ei;
    for(int i=1;i<=N-1;i++)ans/=i;
    for(int i=0;i<N-1;i++)ans/=C;
    printf("%.20f\n",ans);
    return 0;
}
