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[] freq = new int[101];
            for (int i = 0; i < n; i++) {
                int a_i = in.nextInt();
                freq[a_i] = freq[a_i] + 1;
            }
            
            int max = freq[0] + freq[1] > 2 ? freq[0] + freq[1] : 2; // the answer will be >= 2
            //check a_i = 0 & 1;
            for (int i = 1; i <= 99; i++) {
                int num = freq[i] + freq[i + 1];
                if (num > max) {
                    max = num;
                }
            }

            System.out.println(max);
    }
}