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 i=0;i<100;i++)
            {
            a[i]=0;
        }
        for(int i=0; i < n; i++){
            int temp = in.nextInt();
            a[temp]=a[temp]+1;
        }
        int max=-1;
        for(int i=0;i<99;i++)
            {
            int temp=a[i]+a[i+1];
            if(temp>max)
                {
                max=temp;
            }
        }
        
        System.out.println(max);
    }
}