题目
AC

import java.util.Scanner;public class Main {public static void main(String[] args) {Scanner sc = new Scanner(System.in);int n = sc.nextInt();if(n>=0) {StringBuilder str = new StringBuilder();str.append(n);StringBuilder str1 = str.reverse();String str2 = str1.toString();int m = Integer.valueOf(str2);System.out.println(m);}else {String str = n+"";String str1 = str.substring(1,str.length());//去掉负号			StringBuilder str2 = new StringBuilder();str2.append(str1);StringBuilder str3 = str2.reverse();		String str4 = str3.toString();int k = Integer.valueOf(str4);k = -k;System.out.println(k);}}	
}