解题思路：

数量级较大，需要使用long类型

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        long num = scan.nextLong();

        long allseconds = num / 1000;
        long seconds = allseconds % 60;

        long allmins = allseconds / 60;
        long mins = allmins % 60;

        long allhours = allmins / 60;
        long hours = allhours % 24;

        String date = String.format("%02d", hours) + ":" + String.format("%02d", mins) + ":" +
                String.format("%02d", seconds);
        System.out.println(date);
    }
}