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();
        Map<Integer, Integer> map = new HashMap<Integer, Integer>();
        for (int i = 0; i < n; i++){
            int m = in.nextInt();
            if (!map.containsKey(m))
                map.put(m, 0);
            map.put(m, map.get(m)+1);
        }
        int max = 0;
        for (int i : map.keySet()){
            int count = map.get(i);
            if (map.containsKey(i+1))
                count += map.get(i+1);
            if (count > max) max = count;
        }
        System.out.println(max);
    }
}