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];
        for(int a_i=0; a_i < n; a_i++){
            a[a_i] = in.nextInt();
        }
        int max = 0;
        for(int i = 0; i < n; i++) {
            int element = a[i];
            int element2 = a[i];
            int count = 0;
            int c = 0;
            for(int j = 0; j < n; j++) {
                if(i == j) {
                    continue;
                }
                if(c == 1) {
                    if(a[j] == element || a[j] == element2) {
                        count++;
                        continue;
                    }
                }
                if(Math.abs(a[i] - a[j]) == 1 && c == 0) {
                    c = 1;
                    count++;
                    element2 = a[j];
                }
                if(Math.abs(a[i] - a[j]) == 0 && c == 0) {
                    count++;
                }
            }
            if(count != 0 && count + 1 > max) {
                max = count + 1;
            }
        }
        System.out.println(max);
    }
}