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 max=0,count=1,flag=0,count_1=0;
        int[] a = new int[n];
        for(int a_i=0; a_i < n; a_i++){
            a[a_i] = in.nextInt();
        }
        Arrays.sort(a);
        
        for(int i=1;i<n;i++){
            if(a[i]==a[i-1] ){
                if(flag==0)
                count++;
                else
                    count_1++;
            }
            else if(a[i]==a[i-1]+1 && flag==0){
                flag=1;
                count_1++;
            }
            else{
                if(max<count_1+count){
                    max=count+count_1;
                }
                if(a[i]==a[i-1]+1){  
                     count=count_1;
                    count_1=0;
                    i--;
                    flag=0;
                }
               else if(a[i]>a[i-1]+1){
                   count=1;
                   count_1=0;
                   
                   flag=0;
               }
                    
                }
            }
        if(count+count_1>max){
            max=count+count_1;
        }
        System.out.println(max);
    }
}