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[100];
        int i,count=0;
        for(int a_i=0; a_i < n; a_i++){
            i = in.nextInt();
            a[i]++;
            if(i!=1 && i!=99){
                if(a[i] + a[i+1] > count){
                    count = a[i]+a[i+1];
                }
                if(a[i] + a[i-1] > count){
                    count = a[i] + a[i-1];
                }
                
            }else if(i==1){
               if(a[i] + a[i+1] > count){
                    count = a[i]+a[i+1];
                }
            }else if(i == 99){
                if(a[i] + a[i-1] > count){
                    count = a[i] + a[i-1];
                }
            }
        }
        System.out.println(count);
    }
}