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

}