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[] map = new int[101];
        
        int[] a = new int[n];
        for(int a_i=0; a_i < n; a_i++){
            a[a_i] = in.nextInt();
            map[a[a_i]]++;
            
        }
        
        int max = 0;
        for (int i = 1; i < map.length-1; i++) {
            max = Math.max(max, Math.max(map[i] + map[i-1], map[i] + map[i+1]));
        }
        System.out.println(max);
    }
    
    
}