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();
		}

		ArrayList<Integer> score = new ArrayList<Integer>();
		int count = 0;
		int plusOrMinus = 0;

		for (int i = 0; i < a.length; i++) {
			for (int j = 0; j < a.length; j++) {

				count = 0;
				plusOrMinus = 0;
				for (int k = j; k < a.length; k++) {

					if (i != j) {

						if (a[i] - a[k] == 1 && plusOrMinus == 0) {
							plusOrMinus = 1;
							count++;
						} else {
							if (a[i] - a[k] == -1 && plusOrMinus == 0) {
								plusOrMinus = -1;
								count++;
							} else {

								if (a[i] - a[k] == 0) {
									count++;
								} else {

									if (a[i] - a[k] == -1 && plusOrMinus == -1) {
										count++;
									} else {
										if (a[i] - a[k] == 1 && plusOrMinus == 1) {
											count++;
										}

									}
								}
							}
						}
					}

				}

				score.add(count);

			}

		}

		int max = Collections.max(score);
		System.out.println(max);

	}

}