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[] b = new int[1001];
        for(int a_i=0; a_i < n; a_i++){
            a[a_i] = in.nextInt();
            b[a[a_i]]++;
        }
        int max = 0;
        for(int i=0; i<1000; i++){
            if(b[i]!=0){
                int sum = b[i];
                if(sum>max)
                    max=sum;
            }
            if(b[i]!=0 && b[i+1]!=0){
                int sum = b[i]+b[i+1];
                if(sum>max)
                    max=sum;
            }
        }
        System.out.println(max);
    }
    
}