import java.io.*;
public class abcd {
	
	public static void main(String args[])throws IOException{
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		int N = Integer.parseInt(br.readLine());
		String s = br.readLine();
		String ss[] = s.split(" ");
		int arr[];
		arr = new int[100];
		
		for(int i=0;i<N;i++)arr[Integer.parseInt(ss[i])]++;
		
		int max = Integer.MIN_VALUE;
		for(int i=0;i<99;i++){
			max = Math.max(max,arr[i]+arr[i+1]);
		}
		System.out.println(max);
		
	}

}