import java.util.*;

class Num{
    int n;
    int Palindrome;
    Num(int n){
        this.n = n;
        this.Palindrome = getPal();
    }
    public int getPal(){
        int left = n-1,right = n+1;
        while(true){
            if(isPal(left)){
                return left;
            }
            if(isPal(right)){
                return right;
            }
            left--;
            right++;
        }
    }
    public boolean isPal(int a){
        int org = a;
        int rev = 0;
        int rem;
        while(org>0){
            rem = org%10;
            rev = rev*10 + rem;
            org/=10;
        }
        return rev == a;
    }
}

public class Main{
    public static void main(String[] args){
        
        Scanner s = new Scanner(System.in);
        String n = s.next();
        
        if(n == null || n.isEmpty() || n.length()>18){
            System.out.println("Invalid input");
            return;
        }
        for(char ch: n) {
            if(!Character.isDigit(ch)){
                System.out.println("Invalid input");
                return;
            }
        }

        Num nn = new Num(Integer.valueOf(n));
        System.out.println(nn.Palindrome);
    }
}