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

class Main
{
	public static boolean eqchar(String s)
	{
		for (int i = 1; i < s.length(); i++)
		{
			if (s.charAt(i) != s.charAt(0)) return false;
		}
		return true;
	}

	public static boolean ispal(String s)
	{
		for (int i = 0; i < s.length()/2; i++)
		{
			if (s.charAt(i) != s.charAt(s.length() - i - 1)) return false;
		}
		return true;
	}
	
	public static void main (String[] args) throws java.lang.Exception
	{
		Scanner in=new Scanner(System.in);
		String s = in.nextLine();
		if (eqchar(s)) System.out.println("NO SOLUTION");
		else
		{
			if (!ispal(s)) System.out.println(s);
			else
			{
				if (s.charAt(0) < s.charAt(1)) System.out.println(s.substring(0, s.length() - 1));
				else System.out.println(s.substring(1));
			}
		}
	}
}