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.io.InputStreamReader;
import java.io.IOException;
import java.io.BufferedReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.util.StringTokenizer;
import java.io.InputStream;
import java.util.Arrays;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.TreeMap;
import java.util.HashSet;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 */
public class MainC {
	public static void main(String[] args) {
		InputStream inputStream = System.in;
		OutputStream outputStream = System.out;
		InputReader in = new InputReader(inputStream);
		PrintWriter out = new PrintWriter(outputStream);
		TaskC solver = new TaskC();
		solver.solve(1, in, out);
		out.close();
	}
}

class TaskC {
    public int max = 0;
    int[] gems;

	public void solve(int testNumber, InputReader in, PrintWriter out) {
        int n = in.nextInt();
        int d = in.nextInt();

        gems = new int[30001];
        for (int i = 0; i < n; ++i) gems[in.nextInt()]++;

        // rows: start, columns: previous jump
        int[][] dp = new int[30001][500];
        for (int i = 0; i < 30001; ++i) {
            for (int j = 0; j < 500; ++j) {
                dp[i][j] = -1;
            }
        }
        dp[d][250] = gems[d];
        max = gems[d];

        for (int i = d; i < 30001; ++i) {
            // d + j is the distance of the jump to reach here
            for (int j = -250; j < 250; ++j) {
                for (int k = -1; k <= 1; ++k) {
                    // Location after jumping again
                    // d + j + k is the jump length
                    // but we add an offset of +250 in the array index
                    // and don't include d
                    int index = i+d+j+k;
                    if (d+j+k <= 0) continue;
                    if (index >= 30001) break;
                    if (dp[i][j+250] == -1) continue;
                    
                    dp[index][j+k+250] = Math.max(dp[index][j+k+250], dp[i][j+250]+gems[index]);
                    max = Math.max(max, dp[index][j+k+250]);
                }
            }
        }

        out.write(max + "\n");
        
    }

}

class InputReader {
    public BufferedReader reader;
    public StringTokenizer tokenizer;

    public InputReader(InputStream stream) {
        reader = new BufferedReader(new InputStreamReader(stream), 32768);
        tokenizer = null;
    }

    public String next() {
        while (tokenizer == null || !tokenizer.hasMoreTokens()) {
            try {
                tokenizer = new StringTokenizer(reader.readLine());
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
        return tokenizer.nextToken();
    }

    public int nextInt() {
        return Integer.parseInt(next());
    }
    public long nextLong() {
        return Long.parseLong(next());
    }

}