题解 | #动态字符串#

import java.util.Scanner;

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);
        for(int i=sb.length()-3;i>=0;i-=3){
            sb.insert(i,',');
        }
        System.out.print(sb.toString());
        

    }
}