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......
        StringBuilder sc = new StringBuilder(str);
        for(int i = str.length()-3;i>=0;i-=3){
            sc.insert(i,",");
        }
        System.out.println(sc);
    }
}