Problem: There is a road with length l meters. The start of the road has coordinate 0, the end of the road has coordinate l.

There are two cars, the first standing at the start of the road and the second standing at the end of the road. They will start driving simultaneously. The first car will drive from the start to the end and the second car will drive from the end to the start.

Initially, they will drive with a speed of 1 meter per second. There are n flags at different coordinates a_1, a_2, …, a_n. Each time when any of two cars drives through a flag, the speed of that car increases by 1 meter per second.

Find how long will it take for cars to meet (to reach the same coordinate). 

Input

The first line contains one integer t (1 ≤ t ≤ 10^4): the number of test cases.

The first line of each test case contains two integers n, l (1 ≤ n ≤ 10^5, 1 ≤ l ≤ 10^9): the number of flags and the length of the road.

The second line contains n integers a_1, a_2, …, a_n in the increasing order (1 ≤ a_1 < a_2 < … < a_n < l).

It is guaranteed that the sum of n among all test cases does not exceed 10^5.

Output

For each test case print a single real number: the time required for cars to meet.

Your answer will be considered correct, if its absolute or relative error does not exceed 10^{-6}. More formally, if your answer is a and jury's answer is b, your answer will be considered correct if \frac{|a-b|}{max{(1, b)}} ≤ 10^{-6}.

Example

Input


5
2 10
1 9
1 10
1
5 7
1 2 3 4 6
2 1000000000
413470354 982876160
9 478
1 10 25 33 239 445 453 468 477


Output


3.000000000000000
3.666666666666667
2.047619047619048
329737645.750000000000000
53.700000000000000

Note

In the first test case cars will meet in the coordinate 5.

The first car will be in the coordinate 1 in 1 second and after that its speed will increase by 1 and will be equal to 2 meters per second. After 2 more seconds it will be in the coordinate 5. So, it will be in the coordinate 5 in 3 seconds.

The second car will be in the coordinate 9 in 1 second and after that its speed will increase by 1 and will be equal to 2 meters per second. After 2 more seconds it will be in the coordinate 5. So, it will be in the coordinate 5 in 3 seconds.

In the second test case after 1 second the first car will be in the coordinate 1 and will have the speed equal to 2 meters per second, the second car will be in the coordinate 9 and will have the speed equal to 1 meter per second. So, they will meet after (9-1)/(2+1) = 8/3 seconds. So, the answer is equal to 1 + 8/3 = 11/3.

Solution (in JAVA):

Solution:
//import com.sun.org.apache.xpath.internal.operations.String;

//import com.sun.org.apache.xpath.internal.operations.String;

import java.io.*;
import java.math.BigDecimal;
import java.math.BigInteger;
import java.math.RoundingMode;
import java.util.*;


public class scratch_25 {
    // int count=0;
    //static long count=0;
    static class Reader {
        static BufferedReader reader;
        static StringTokenizer tokenizer;

        /**
         * call this method to initialize reader for InputStream
         */
        static void init(InputStream input) {
            reader = new BufferedReader(
                    new InputStreamReader(input));
            tokenizer = new StringTokenizer("");
        }

        /**
         * get next word
         */
        static String next() throws IOException {
            while (!tokenizer.hasMoreTokens()) {
                //TODO add check for eof if necessary
                tokenizer = new StringTokenizer(
                        reader.readLine());
            }
            return tokenizer.nextToken();
        }

        static int nextInt() throws IOException {
            return Integer.parseInt(next());
        }

        static double nextDouble() throws IOException {
            return Double.parseDouble(next());
        }

        static long nextLong() throws IOException {
            return Long.parseLong(next());
        }
    }

    public static class Graph{
        public static class Vertex{
            HashMap<Integer,Integer> nb= new HashMap<>();     // for neighbours of each vertex
        }

        public static HashMap<Integer,Vertex> vt;   // for vertices(all)

        public Graph(){
            vt= new HashMap<>();
        }

        public static int numVer(){
            return vt.size();
        }

        public static boolean contVer(int ver){
            return vt.containsKey(ver);
        }

        public static void addVer(int ver){
            Vertex v= new Vertex();
            vt.put(ver,v);
        }

        public static int numEdg(){
            int count=0;
            ArrayList<Integer> vrtc= new ArrayList<>(vt.keySet());
            for (int i = 0; i <vrtc.size() ; i++) {
                count+=(vt.get(vrtc.get(i))).nb.size();
            }
            return count/2;
        }

        public static boolean contEdg(int ver1, int ver2){
            if(vt.get(ver1)==null || vt.get(ver2)==null){
                return false;
            }

            Vertex v= vt.get(ver1);
            if(v.nb.containsKey(ver2)){
                return true;
            }
            return false;
        }

        public static void addEdge(int ver1, int ver2, int weight){
            if(!vt.containsKey(ver1) || !vt.containsKey(ver2)){
                return;
            }
            Vertex v1= vt.get(ver1);
            Vertex v2= vt.get(ver2);
            v1.nb.put(ver2,weight);                                 // if previously there is an edge, then this replaces that edge
            v2.nb.put(ver1,weight);
        }

        public static void delEdge(int ver1, int ver2){

            if(!vt.containsKey(ver1) || !vt.containsKey(ver2)){
                return;
            }

            vt.get(ver1).nb.remove(ver2);
            vt.get(ver2).nb.remove(ver1);

        }

        public static void delVer(int ver){
            if(!vt.containsKey(ver)){
                return;
            }
            Vertex v1= vt.get(ver);
            ArrayList<Integer> arr= new ArrayList<>(v1.nb.keySet());
            for (int i = 0; i <arr.size() ; i++) {
                int s= arr.get(i);
                vt.get(s).nb.remove(ver);
            }
            vt.remove(ver);
        }

        public class Pair{
            int vname;
            ArrayList<Integer> psf= new ArrayList<>();       // path so far
            int dis;
            int col;
        }









        public HashMap<Integer,Integer> bfs(int src){
            HashMap<Integer, Boolean> prcd= new HashMap<>();    // jo jo ho chuke hain unke liye

            HashMap<Integer, Integer> ans= new HashMap<>();

            LinkedList<Pair> queue= new LinkedList<>();      // for bfs queue

            Pair strtp= new Pair();

            strtp.vname= src;

            ArrayList<Integer> ar= new ArrayList<>();
            ar.add(src);

            strtp.psf= ar;
            strtp.dis=0;

            queue.addLast(strtp);

            while(!queue.isEmpty()){

                Pair rp =  queue.removeFirst();

                if(prcd.containsKey(rp.vname)){
                    continue;
                }
                prcd.put(rp.vname,true);
                ans.put(rp.vname,rp.dis);

//                if(contEdg(rp.vname,dst)){
//                    return true;
//                }

                Vertex a= vt.get(rp.vname);
                ArrayList<Integer> arr= new ArrayList<>(a.nb.keySet());
                for (int i = 0; i <arr.size() ; i++) {
                    int s= arr.get(i);
                    if(!prcd.containsKey(s)){
                        Pair np = new Pair();
                        np.vname= s;
                        np.dis+=rp.dis+a.nb.get(s);
                        np.psf.addAll(rp.psf);
                        np.psf.add(s);
//                        np.psf.add(s);
//                         np.psf= rp.psf+" "+s;
                        queue.addLast(np);
                    }

                }
            }
            return ans;

            //   return false;
        }








        public HashMap<Integer,Integer> dfs(int src){
            HashMap<Integer, Boolean> prcd= new HashMap<>();    // jo jo ho chuke hain unke liye

            HashMap<Integer, Integer> ans= new HashMap<>();

            LinkedList<Pair> stack= new LinkedList<>();      // for bfs queue

            Pair strtp= new Pair();

            strtp.vname= src;

            ArrayList<Integer> ar= new ArrayList<>();
            ar.add(src);

            strtp.psf= ar;
            strtp.dis=0;

            stack.addFirst(strtp);

            while(!stack.isEmpty()){

                Pair rp =  stack.removeFirst();

                if(prcd.containsKey(rp.vname)){
                    continue;
                }
                prcd.put(rp.vname,true);
                ans.put(rp.vname,rp.dis);

//                if(contEdg(rp.vname,dst)){
//                    return true;
//                }

                Vertex a= vt.get(rp.vname);
                ArrayList<Integer> arr= new ArrayList<>(a.nb.keySet());
                for (int i = 0; i <arr.size() ; i++) {
                    int s= arr.get(i);
                    if(!prcd.containsKey(s)){
                        Pair np = new Pair();
                        np.vname= s;
                        np.dis+=rp.dis+a.nb.get(s);
                        np.psf.addAll(rp.psf);
                        np.psf.add(s);
//                        np.psf.add(s);
//                         np.psf= rp.psf+" "+s;
                        stack.addFirst(np);
                    }

                }
            }
            return ans;

            //   return false;
        }






        public boolean isCycle(){
            HashMap<Integer, Boolean> prcd= new HashMap<>();    // jo jo ho chuke hain unke liye

            //   HashMap<Integer, Integer> ans= new HashMap<>();

            LinkedList<Pair> queue= new LinkedList<>();      // for bfs queue



            ArrayList<Integer> keys = new ArrayList<>(vt.keySet());
            for (int i = 0; i <keys.size(); i++) {
                int cur= keys.get(i);
                if(prcd.containsKey(cur)){
                    continue;
                }

                Pair sp = new Pair();
                sp.vname= cur;
                ArrayList<Integer> as= new ArrayList<>();
                as.add(cur);
                sp.psf= as;

                queue.addLast(sp);

                while(!queue.isEmpty()){




                    Pair rp= queue.removeFirst();
                    if(prcd.containsKey(rp.vname)){
                        return true;
                    }

                    prcd.put(rp.vname,true);




                    Vertex v1= vt.get(rp.vname);
                    ArrayList<Integer> nbrs= new ArrayList<>(v1.nb.keySet());
                    for (int j = 0; j <nbrs.size() ; j++) {
                        int u= nbrs.get(j);
                        Pair np= new Pair();
                        np.vname= u;
                        queue.addLast(np);
                    }
                }

            }
            return false;
        }






        public  ArrayList<ArrayList<Integer>> genConnctdComp(){
            HashMap<Integer, Boolean> prcd= new HashMap<>();    // jo jo ho chuke hain unke liye

            ArrayList<ArrayList<Integer>> ans= new ArrayList<>();

            //   HashMap<Integer, Integer> ans= new HashMap<>();

            LinkedList<Pair> queue= new LinkedList<>();      // for bfs queue

            //  int con=-1;

            ArrayList<Integer> keys = new ArrayList<>(vt.keySet());
            for (int i = 0; i <keys.size(); i++) {
                int cur= keys.get(i);
                if(prcd.containsKey(cur)){
                    //return true;
                    continue;
                }
                int count=0;
                ArrayList<Integer> fu= new ArrayList<>();
                fu.add(cur);


                Pair sp = new Pair();
                sp.vname= cur;
                ArrayList<Integer> as= new ArrayList<>();
                as.add(cur);
                sp.psf= as;

                queue.addLast(sp);

                while(!queue.isEmpty()){




                    Pair rp= queue.removeFirst();
                    if(prcd.containsKey(rp.vname)){
                        //return true;
                        continue;
                    }

                    prcd.put(rp.vname,true);
                    fu.add(rp.vname);



                    Vertex v1= vt.get(rp.vname);
                    ArrayList<Integer> nbrs= new ArrayList<>(v1.nb.keySet());
                    for (int j = 0; j <nbrs.size() ; j++) {
                        int u= nbrs.get(j);
                        if(!prcd.containsKey(u)){
                            count++;
                            Pair np= new Pair();
                            np.vname= u;
                            queue.addLast(np);
                        }
                    }}
                fu.add(count);
                ans.add(fu);

            }
            //return false;
            return ans;

        }

        public boolean isBip(int src){                       // only for connected graph

            HashMap<Integer,Integer> clr= new HashMap<>();
            // colors are 1 and -1


            LinkedList<Integer>q = new LinkedList<Integer>();
            clr.put(src,1);
            q.add(src);


            while(!q.isEmpty()){

                int u = q.getFirst();
                q.pop();

                ArrayList<Integer> arr= new ArrayList<>(vt.keySet());

                for (int i = 0; i <arr.size() ; ++i) {

                    int x= arr.get(i);

                    if(vt.get(u).nb.containsKey(x) && !clr.containsKey(x)){

                        if(clr.get(u)==1){
                            clr.put(x,-1);
                        }
                        else{
                            clr.put(x,1);
                        }
                        q.push(x);
                    }

                    else if(vt.get(u).nb.containsKey(x) && (clr.get(x).equals(clr.get(u)))){
                        return false;
                    }

                }
            }
            return true;
        }

















        public static void printGr() {
            ArrayList<Integer> arr= new ArrayList<>(vt.keySet());
            for (int i = 0; i <arr.size() ; i++) {
                int ver= arr.get(i);
                Vertex v1= vt.get(ver);
                ArrayList<Integer> arr1= new ArrayList<>(v1.nb.keySet());
                for (int j = 0; j <arr1.size() ; j++) {
                    System.out.println(ver+"-"+arr1.get(j)+":"+v1.nb.get(arr1.get(j)));
                }

            }
        }
    }

    static class Cus implements Comparable<Cus>{
        int size;
        int mon;
        int num;
        public Cus(int size,int mon,int num){
            this.size=size;
            this.mon=mon;
            this.num=num;
        }
        @Override
        public int compareTo(Cus o){
            if(this.mon!=o.mon){
                return this.mon-o.mon;}

            else{
                return o.size-this.size;
            }

        }



    }

    static class Lamp implements Comparable<Lamp>{
        long start ;
        //  int cum;
        long end;
        public Lamp(long start,long end){
            this.start=start;
            //    this.cum=cum;
            this.end=end;
        }
        @Override
        public int compareTo(Lamp o){

            return (int)this.start-(int)o.start;

        }


    }

    static class Event implements Comparable<Event>{
        int value;
        int dist;
        public Event(int value,int dist){
            this.value=value;
            this.dist= dist;
        }

        @Override
        public int compareTo(Event o){

        if(this.dist!=o.dist){
          return this.dist-o.dist;}

        else{
            return this.value-o.value;
        }


          //  return (int)this.state-(int)o.state;


        }






    }
    static class Table1 implements Comparable<Table1>{
        int go;
        //int cum;
        int cost;
        public Table1(int go,int cost){
            this.go=go;
            //  this.cum=cum;
            this.cost=cost;
        }
        @Override
        public int compareTo(Table1 o){
            return this.cost-o.cost;


        }}

    public static class DisjointSet{
        HashMap<Integer,Node> mp= new HashMap<>();

        public static class Node{
            int data;
            Node parent;
            int rank;
        }


        public void create(int val){
            Node nn= new Node();
            nn.data=val;
            nn.parent=nn;
            nn.rank=0;
            mp.put(val,nn);
        }

        public int find(int val){

            return findn(mp.get(val)).data;

        }


        public Node findn(Node n){
            if(n==n.parent){
                return n;
            }
            Node rr= findn(n.parent);
            n.parent=rr;
            return rr;
        }



        public void union(int val1, int val2){                                                                               // can also be used to check cycles

            Node n1= findn(mp.get(val1));
            Node n2= findn(mp.get(val2));


            if(n1.data==n2.data) {
                return;
            }



            if(n1.rank<n2.rank){
                n1.parent=n2;
            }

            else if(n2.rank<n1.rank){
                n2.parent=n1;
            }

            else {
                n2.parent=n1;
                n1.rank++;
            }

        }
    }







    public static void main(String[] args)  throws IOException {
        Reader.init(System.in);
        BufferedWriter out = new BufferedWriter(new OutputStreamWriter(System.out));
       int t =Reader.nextInt();
        for (int i = 0; i <t ; i++) {

            int n= Reader.nextInt();
            int l= Reader.nextInt();
            long arr[]= new long[n+2];
            double time=0;
            arr[0]=0;
            arr[n+1]=l;

            for (int j = 1; j <n+1 ; j++) {
                arr[j]= Reader.nextLong();
            }

         //   System.out.println(Arrays.toString(arr));

            int p1=0;
            int p2=n+1;

            long s1=1;
            long s2=1;

            double pr1=0;
            double pr2=l;

            while(p2-p1>1){




                double min1= (1.0*arr[p1+1]-pr1)/s1;
                double min2=(pr2-1.0*arr[p2-1])/s2;


                if(min1<min2){


                    double t1= (1.0*min1);
                    time+=t1;
                    s1++;

                    pr1=arr[p1+1];
                    pr2-=s2*t1;
                    while(pr1>arr[p1+1]){
                        p1++;
                    }
                    p1++;
                }
                else{

                    double t1=(1.0*min2);
                    time+=t1;
                    s2++;
                    pr2=arr[p2-1];
//                    System.out.print(" fucki "+pr1+" ");
//                    System.out.print(" speed="+s1+" time="+t1+" s*t="+s1*t1);
                    pr1+=t1*s1;
                   // System.out.print(pr1);
                    while(pr2<arr[p2-1]){
                        p2--;
                    }
                    p2--;
                }

//                System.out.print("time= "+time);
//                System.out.print(" p1= "+p1);
//                System.out.print(" p2="+p2);
//                System.out.print(" s1="+s1);
//                System.out.print(" s2="+s2);
//                System.out.println(" pr1="+pr1 +" pr2="+pr2);


            }

//            System.out.println("pr1="+pr1);
//            System.out.println("pr2="+pr2);









            time+=(1.0*(pr2-pr1))/(1.0*(s1+s2));

            String secondNumberAsString = String.format("%.10f",time);

            System.out.println(secondNumberAsString);






















        }





    }
    static long power( long x, long y, long p)
    {
        // Initialize result
        long res = 1;

        // Update x if it is more
        // than or equal to p
        x = x % p;

        if (x == 0) return 0; // In case x is divisible by p;

        while (y > 0)
        {
            // If y is odd, multiply x
            // with result
            if((y & 1)==1)
                res = (res * x) % p;

            // y must be even now
            // y = y / 2
            y = y >> 1;
            x = (x * x) % p;
        }
        return res;
    }

    public static long ceil_div(long a, long b){
        return (a+b-1)/b;
    }

    static int countDivisibles(int A, int B, int M)
    {
        // Add 1 explicitly as A is divisible by M
        if (A % M == 0)
            return (B / M) - (A / M) + 1;

        // A is not divisible by M
        return (B / M) - (A / M);
    }


    public static void df(int x, int y,int n, int m, char[][]ar, int l){
        boolean done[][]= new boolean[n][m];
        int count=0;
        LinkedList<int[]> stk= new LinkedList<>();
        int a[]= {x,y};
        stk.addFirst(a);
        while(!stk.isEmpty() && count<l){
            //  count++;
            int b[]=stk.removeFirst();
            if( done[b[0]][b[1]]){
                continue;
            }
            count++;

            done[b[0]][b[1]]=true;
            ar[b[0]][b[1]]='@';
            int arr[][]={{1,0},{-1,0},{0,1},{0,-1}};
            for (int i = 0; i <arr.length ; i++) {
                if(!(b[0]+arr[i][0]>=n || b[1]+arr[i][1]>=m || b[0]+arr[i][0]<0 || b[1]+arr[i][1]<0 ||  ar[b[0]+arr[i][0]][b[1]+arr[i][1]]=='#')){
                    int r[]= {b[0]+arr[i][0], b[1]+arr[i][1]};
                    stk.addFirst(r);
                    // continue;



                }
            }}


        for (int i = 0; i <n ; i++) {
            for (int j = 0; j <m ; j++) {
                if(ar[i][j]=='.'){
                    System.out.print('X');
                }
                else if(ar[i][j]=='@'){
                    System.out.print('.');
                }
                else{
                    System.out.print(ar[i][j]);
                }
            }
            System.out.println();
        }
























    }











    static long gcd(long a, long b)
    {
        if (a == 0)
            return b;
        return gcd(b % a, a);
    }



    static long gcd1(long a, long b)
    {

        // Everything divides 0
        if (a == 0)
            return b;
        if (b == 0)
            return a;

        // base case
        if (a == b)
            return a;

        // a is greater
        //count++;
        if (a > b){
            return gcd(a-b, b);

        }
        return gcd(a, b-a);
    }





    // method to return LCM of two numbers
    static long lcm(long a, long b)
    {
        return (a*b)/gcd(a, b);
    }

    // Driver method

    static int partition(long arr[],long arr1[], int low, int high)
    {
        long pivot = arr[high];
        int i = (low-1); // index of smaller element
        for (int j=low; j<high; j++)
        {
            // If current element is smaller than the pivot
            if (arr[j] < pivot)
            {
                i++;

                // swap arr[i] and arr[j]
                long temp = arr[i];
                arr[i] = arr[j];
                arr[j] = temp;
                long temp1=arr1[i];
                arr1[i]=arr1[j];
                arr1[j]=temp1;

            }
        }

        // swap arr[i+1] and arr[high] (or pivot)
        long temp = arr[i+1];
        arr[i+1] = arr[high];
        arr[high] = temp;
        long temp1= arr1[i+1];
        arr1[i+1]=arr1[high];
        arr1[high]= temp1;

        return i+1;
    }


    /* The main function that implements QuickSort()
      arr[] --> Array to be sorted,
      low  --> Starting index,
      high  --> Ending index */
    static void sort(long arr[],long arr1[], int low, int high)
    {
        if (low < high)
        {
            /* pi is partitioning index, arr[pi] is
              now at right place */
            int pi = partition(arr,arr1, low, high);

            // Recursively sort elements before
            // partition and after partition
            sort(arr,arr1, low, pi-1);
            sort(arr,arr1, pi+1, high);
        }
    }







































































    public static ArrayList<Integer> Sieve(int n) {
        boolean arr[]= new boolean [n+1];
        Arrays.fill(arr,true);
        arr[0]=false;
        arr[1]=false;
        for (int i = 2; i*i <=n ; i++) {
            if(arr[i]){
                for (int j = 2; j <=n/i ; j++) {
                    int u= i*j;
                    arr[u]=false;
                }}
        }
        ArrayList<Integer> ans= new ArrayList<>();
        for (int i = 0; i <n+1 ; i++) {
            if(arr[i]){
                ans.add(i);
            }
        }
        return ans;










    }





}