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[] count = new int[100];
        int item;
        for(int a_i=0; a_i < n; a_i++){
            item = in.nextInt();
            a[a_i] = item;
            count[item]++;
        }
        int max = count[1] + count[2];
        for(int i=2;i<99;i++)
        {
            int val = count[i] + count[i+1];
            max = (val>max)?val:max;
        }
        System.out.println(max);
    }
}