import java.util.*;

public class Main {

	public static int solution(int[] arr) {

		int length = 0;
		for(int i = 0 ; i < arr.length ; i++){
		    int max = Integer.MIN_VALUE;
		    int min = Integer.MAX_VALUE;
		    
		    //HS to check duplicacy 
		    HashSet<Integer> set = new HashSet<>();
		    for(int j =i  ; j < arr.length ;j++ ){
		        max = Math.max(arr[j],max);
		        min = Math.min(arr[j],min);
		        
		        if(set.contains(arr[j])) break;
		        
		        set.add(arr[j]);
		        
		        //contiguous element trick 
		        int val1 = max - min;
		        int val2 = j-i;
		        
		        if(val1 == val2){
		            int potential = j -i +1;
		            
		            if(length < potential)
		            length = potential;
		        }
		        
		        //if max - min becomes more than no.of indexes break;
		        if(val1 > arr.length)break;
		    }
		}

		return length;
	}
	
	public static void main(String[] args) {
		Scanner scn = new Scanner(System.in);
		int[] arr = new int[scn.nextInt()];
		for (int i = 0; i < arr.length; i++) {
			arr[i] = scn.nextInt();
		}
		System.out.println(solution(arr));
	}

}