import java.util.*;
public class Main
{
    public static boolean isPalindrome(int n)
    {
        int origin=n;
        int rev=0;
        while(n>0)
        {
            int d=n%10;
            rev=rev*10+d;
            n=n/10;
        }
        return origin==rev;
    }
    public static void main(String[] args)
    {
        Scanner sc=new Scanner(System.in);
        String str=sc.next();
        if(str==null||str.isEmpty()||str.length()>18)
        {
            System.out.print("Invalid input");
            return;
        }
        if(!sc.hasnextInt())
        {
            System.out.print("Invalid input");
            return;
        }
        int n=Integer.parseInt(str);
        int low=n-1;
        while(low>0)
        {
            if(isPalindrome(low))
            {
                System.out.println(low);
                return;
            }
            low--;
        }
    }
}