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];
        int min = 1;
        int low = 0;
        for(int a_i=0; a_i < n; a_i++){
            a[a_i] = in.nextInt();
        }
        //another method is just to use a hashmap and map the number of times number appears
        //find the largest one and add the next consecutive value
        //because if each value appears once the max is always 2 numbers in a set to keep the <= 1 difference
        Arrays.sort(a);
        int count = 1;
        int prev = 0; //previous number count
        int curr = 1; //current number count
        for(int i = 1; i < n; i++){
            if(a[i] == a[i-1]){
                curr++;
                if((prev + curr) > count){
                    count = prev + curr;
                }
            }
            else if(a[i] - 1 == a[i-1]){
                prev = curr;
                curr = 1;
                if((prev + curr) > count){
                    count = prev + curr;
                }
            }
            else{
                prev = 0;
                curr = 1;
            }
        }
        System.out.println(count);
    }
}