直接反向打印就可以

import java.util.*;
public class Main {
        public static void main(String[] args) {
            Scanner sc= new Scanner(System.in);
            while (sc.hasNextLine()) {
                String str = sc.nextLine();
                int length = str.length();
                for (int i = length -1; i >=0; i--) {
                    System.out.print(str.charAt(i));
                }
            }
        }
}