import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int[] a = new int[n];
        for(int a_i=0; a_i < n; a_i++){
            a[a_i] = in.nextInt();
        }
        int count = 0;
        HashMap<Integer, Set<Integer>> numbers = new HashMap<Integer, Set<Integer>>();
        int max = -1;
        for (int i = 0; i<a.length-1; i++) {
            for (int j = 0; j<a.length; j++) {
                int val = a[i] - a[j];
                if (val == 0 || val == 1 ) {
                    if (!numbers.containsKey(a[i])) {
                        numbers.put(a[i], new HashSet<Integer>());
                    }
                    Set<Integer> nums = numbers.get(a[i]);
                    nums.add(j);
                    if (nums.size()> max) {
                        max = nums.size();
                    }
                    numbers.put(a[i], nums);
                }
            }
        }
        System.out.println(max);
    }
}