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......
        String res;
        int len = str.length();
        int index = len % 3;
        res = str.substring(0, index);

        while (index + 3 <= len){
            res = res + "," + str.substring(index, index+3);
            index += 3;
        }
        System.out.println(res);

    }
}