import java.util.*;
public class Solution {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub

		Scanner sc=new Scanner(System.in);
		
		int n=sc.nextInt();
		
		int[] arr=new int[100];
		for(int i=0;i<n;i++){
			int x=sc.nextInt();
			arr[x]++;
		}
		int sum=0;
		for(int i=0;i<100;i++){
			if(i<n-1 && arr[i]+arr[i+1]>sum){
				sum=arr[i]+arr[i+1];
			}
		}
		System.out.println(sum);
	}
}