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];
        
        for(int a_i=0; a_i < n; a_i++)
        {
            int an= in.nextInt();
            a[an]++;
        }
        
        int max=0;
        for(int i=2;i<100;i++)
        {
            if(a[i]+a[i-1]>max) max=a[i]+a[i-1];
        }
        System.out.println(max);
    }
}