Problem: The Shuseki Islands are an archipelago of 30001 small islands in the Yutampo Sea. The islands are evenly spaced along a line, numbered from 0 to 30000 from the west to the east. These islands are known to contain many treasures. There are n gems in the Shuseki Islands in total, and the i-th gem is located on island pi.

Mr. Kitayuta has just arrived at island 0. With his great jumping ability, he will repeatedly perform jumps between islands to the east according to the following process: 

  * First, he will jump from island 0 to island d. 
  * After that, he will continue jumping according to the following rule. Let l be the length of the previous jump, that is, if his previous jump was from island prev to island cur, let l = cur - prev. He will perform a jump of length l - 1, l or l + 1 to the east. That is, he will jump to island (cur + l - 1), (cur + l) or (cur + l + 1) (if they exist). The length of a jump must be positive, that is, he cannot perform a jump of length 0 when l = 1. If there is no valid destination, he will stop jumping. 



Mr. Kitayuta will collect the gems on the islands visited during the process. Find the maximum number of gems that he can collect.

Input

The first line of the input contains two space-separated integers n and d (1 ≤ n, d ≤ 30000), denoting the number of the gems in the Shuseki Islands and the length of the Mr. Kitayuta's first jump, respectively.

The next n lines describe the location of the gems. The i-th of them (1 ≤ i ≤ n) contains a integer pi (d ≤ p1 ≤ p2 ≤ ... ≤ pn ≤ 30000), denoting the number of the island that contains the i-th gem.

Output

Print the maximum number of gems that Mr. Kitayuta can collect.

Examples

Input

4 10
10
21
27
27


Output

3


Input

8 8
9
19
28
36
45
55
66
78


Output

6


Input

13 7
8
8
9
16
17
17
18
21
23
24
24
26
30


Output

4

Note

In the first sample, the optimal route is 0  →  10 (+1 gem)  →  19  →  27 (+2 gems)  → ...

In the second sample, the optimal route is 0  →  8  →  15  →  21 →  28 (+1 gem)  →  36 (+1 gem)  →  45 (+1 gem)  →  55 (+1 gem)  →  66 (+1 gem)  →  78 (+1 gem)  → ...

In the third sample, the optimal route is 0  →  7  →  13  →  18 (+1 gem)  →  24 (+2 gems)  →  30 (+1 gem)  → ...

Solution (in JAVA):

Solution:
import java.util.*;
import java.io.*;
import static java.lang.Math.*;
import static java.lang.System.*;
public class dp1
{
    public static void main(String[]args){
        InputReader sc = new InputReader(System.in);
        PrintWriter pw =new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)));
        int []gem=new int[30001];
        int gems=sc.nextInt();
        int d=sc.nextInt();
        for(int i=0;i<gems;i++){
        	gem[sc.nextInt()]++;
        }
        int lesser=d;
        int ctr=0;
        while(ctr<30005){
        	ctr+=lesser;
        	if(lesser==1)break;
        	lesser--;
        }
        ctr=0;
        int morer=d;
        while(ctr<30005){
        	ctr+=morer;
        	morer++;
        }
        int[][]dp=new int[30001][morer-lesser+5];
       	//where 0 is lesser. 
       	for(int i=0;i<dp.length;i++){
       		Arrays.fill(dp[i],-1);
       	}
       	dp[d][d-lesser]=gem[d];
       	for(int i=0;i<dp.length-1;i++){
       		for(int a=0;a<dp[i].length;a++){
       			if(dp[i][a]>-1){
       				for(int b=Math.max(1,a+lesser-1);b<=lesser+a+1&&i+b<30001;b++){
       					dp[i+b][b-lesser]=Math.max(dp[i+b][b-lesser],dp[i][a]+gem[i+b]);
       				}
       				
       			}
       		}
       		
       	}
       	int max=-1;
       	for(int i=Math.max(0,dp.length-5-morer);i<dp.length;i++){
       		for(int a=0;a<dp[0].length;a++){
       			max=Math.max(max,dp[i][a]);
       		}
       		
       	}
       	System.out.println(max);
        pw.flush();
    }
    
    static class InputReader
    {
        private final InputStream stream;
        private final byte[] buf = new byte[8192];
        private int curChar, snumChars;
        private SpaceCharFilter filter;
        public InputReader(InputStream stream)
        {
                this.stream = stream;
        }
        public int snext()
        {
                if (snumChars == -1)
                        throw new InputMismatchException();
                if (curChar >= snumChars)
                {
                        curChar = 0;
                        try
                        {
                                snumChars = stream.read(buf);
                        } catch (IOException e)
                        {
                                throw new InputMismatchException();
                        }
                        if (snumChars <= 0)
                                return -1;
                }
                return buf[curChar++];
        }
        public int nextInt()
        {
                int c = snext();
                while (isSpaceChar(c))
                {
                        c = snext();
                }
                int sgn = 1;
                if (c == '-')
                {
                        sgn = -1;
                        c = snext();
                }
                int res = 0;
                do
                {
                        if (c < '0' || c > '9')
                                throw new InputMismatchException();
                        res *= 10;
                        res += c - '0';
                        c = snext();
                } while (!isSpaceChar(c));
                return res * sgn;
        }
        public long nextLong()
        {
                int c = snext();
                while (isSpaceChar(c))
                {
                        c = snext();
                }
                int sgn = 1;
                if (c == '-')
                {
                        sgn = -1;
                        c = snext();
                }
                long res = 0;
                do
                {
                        if (c < '0' || c > '9')
                                throw new InputMismatchException();
                        res *= 10;
                        res += c - '0';
                        c = snext();
                } while (!isSpaceChar(c));
                return res * sgn;
        }
        public double nextDouble()
        {
                int c = snext();
                while (isSpaceChar(c))
                {
                        c = snext();
                }
                int sgn = 1;
                if (c == '-')
                {
                        sgn = -1;
                        c = snext();
                }
                double res = 0;
                while(c<='9'&&c>='0'){
                    res*=10;
                    res+=c-'0';
                    c=snext();
                }
                if(c=='.'){
                    double decimal=0;
                    long multiplier=1;
                    c=snext();
                    do
                    {
                        if (c < '0' || c > '9')
                                throw new InputMismatchException();
                        decimal *= 10;
                        decimal += c - '0';
                        multiplier*=10;
                        c = snext();
                    } while (!isSpaceChar(c));
                    return sgn*(res+decimal/multiplier);
                }else{
                    if(!isSpaceChar(c)){
                        throw new InputMismatchException();
                    }
                    return sgn*res;
                }
        }
        public int[] nextIntArray(int n)
        {
                int a[] = new int[n];
                for (int i = 0; i < n; i++)
                {
                        a[i] = nextInt();
                }
                return a;
        }
        public long[] nextLongArray(int n)
        {
                long a[] = new long[n];
                for (int i = 0; i < n; i++)
                {
                        a[i] = nextLong();
                }
                return a;
        }
        public String next(){return readString();}
        public String readString()
        {
                int c = snext();
                while (isSpaceChar(c))
                {
                        c = snext();
                }
                StringBuilder res = new StringBuilder();
                do
                {
                        res.appendCodePoint(c);
                        c = snext();
                } while (!isSpaceChar(c));
                return res.toString();
        }
        public String nextLine()
        {
                int c = snext();
                StringBuilder res = new StringBuilder();
                do
                {
                        res.appendCodePoint(c);
                        c = snext();
                } while (!isEndOfLine(c));
                if(isEndOfLine(res.charAt(res.length()-1)))
                return res.deleteCharAt(res.length()).toString();
                return res.toString();
        }
        public ArrayList<String> readAll(){
            ArrayList<String>a=new ArrayList<String>();
            try{
                while(true){
                    a.add(nextLine());
                }
            }catch(Exception e){
                
            }
            return a;
        }
        public boolean hasNext(){
            boolean hasnext=true;
            try{
                hasnext= stream.available()!=0;
            }catch(IOException e){
            }
            return hasnext||curChar<snumChars;
        }
        public boolean isSpaceChar(int c)
        {
                if (filter != null)
                        return filter.isSpaceChar(c);
                return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }
        private boolean isEndOfLine(int c)
        {
                return c == '\n' || c == '\r' || c == -1;
        }
        public interface SpaceCharFilter
        {
                public boolean isSpaceChar(int ch);
        }
    }
}