题解 | #动态字符串#

import java.util.Scanner; //运用学到的StringBuffer中的insert方法，并利用一个循环确定插入位置，最后得到所需结果 public class Main { public static void main(String[] args) { Scanner scanner = new Scanner(System.in); String str = scanner.next();

    //write your code here......
    StringBuffer sb = new StringBuffer(str);
    int l = str.length();
    while(l > 0){
        l -= 3;
        if(l < 0) break ;
        sb.insert(l , ',');
        
    }
    System.out.print(sb);
    }

}