import java.util.*;
import java.lang.*;

class Main
{
	
	public static String reverse(String k)
	{
		StringBuilder sb = new StringBuilder();
		for ( int i = k.length() - 1; i >= 0; i-- )
		{
			sb.append( k.charAt( i ) );
		}
		return sb.toString();
	}

	public static int maxMirror( int[] nums )
	{
		int sonuc = 0;
		StringBuilder s = new StringBuilder();
		s.append( ',' );
		for ( int i : nums )
		{
			s.append( i + "," );
		}
		
		
		for ( int i = 0; i < s.toString().length(); i++ )
		{
			int index = 0;
			while ( index < i + 1 )
			{
				String mevzubahis = s.substring( index, i + 1 );
				if ( s.toString().contains( reverse( mevzubahis ) ) && reverse( mevzubahis ).replaceAll( ",", "" ).length() > sonuc && s.charAt( i ) == ',' && s.charAt( index ) == ',' )
				{
					sonuc = reverse( mevzubahis ).replaceAll( ",", "" ).length();
				}
				index++;
			}
		}
		return sonuc;
	}

	/**
	 * @param args
	 */
	public static void main( String[] args )
	{
		int[] nums1 = {1, 2, 3, 8, 9, 3, 2, 1};
		System.out.println(maxMirror(nums1));
		
		int[] nums2 = {1, 2, 1, 4};
		System.out.println(maxMirror( nums2 ));
		
		int[] nums3 = {7, 1, 2, 9, 7, 2, 1};
		System.out.println(maxMirror( nums3 ));
		
		int[] nums4 = {21, 22, 9, 8, 7, 6, 23, 24, 6, 7, 8, 9, 25, 7, 8, 9 };
		System.out.println(maxMirror( nums4 ));
		
	}



}