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[] occ = new int[101];
        for(int a_i=0; a_i < n; a_i++)
        {
            a[a_i] = in.nextInt();
            ++occ[a[a_i]];
        }
        int maxO = 0;
        for(int i=2;i<100;++i)
        {
            if(occ[i]+occ[i-1] > maxO) {    maxO = occ[i]+occ[i-1]; }
        }
        System.out.println(maxO);
    }
}