import java.util.Scanner;

public class Solution {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int[] array = new int[100];
        for (int i = 0; i < 100; i++) {
            array[i] = 0;
        }
        for (int a_i = 0; a_i < n; a_i++) {
            array[in.nextInt()]++;
        }
        int ans = -1;
        for (int i = 0; i < 100; i++) {
            if (i == 0) {
                if (ans < array[i])
                    ans = array[i];
            } else {
                if (ans < array[i] + array[i - 1])
                    ans = array[i] + array[i - 1];
            }
        }
        System.out.println(ans);
    }
}