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[] arr = new int[100];
        for(int a_i=0; a_i < n; a_i++){
            int m=in.nextInt();
            arr[m]++;
        }
        int max=0;
        for(int i=0;i<99;i++)
        {
            if(arr[i]+arr[i+1]>max) max=arr[i]+arr[i+1];
        }
        System.out.println(max);
    }
}