I've tested so many numbers, and it seems right. What's wrong?

Question about the task

Under discussion

package com.codegym.task.task04.task0416;

import java.io.*;

public class Solution
{
    public static void main(String[] args) throws Exception
    {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

        String input1 = reader.readLine();
        double a = Double.parseDouble(input1);

        if(a >= 0 && a < 1)
        {
            System.out.print("green");
        }
        else if(a % 4 >= 0 && a % 4 < 1)
        {
            System.out.print("red");
        }
        else if(++a % 4 >= 0 && a % 4 < 1)
        {
            System.out.print("yellow");
        }
        else
        {
            System.out.print("green");
        }
    }
}

The pedestrian traffic light is programmed as follows:
at the beginning of each hour, the green signal is on for three minutes,
then the signal is yellow for one minute,
and then it is red for one minute.
Then the light is green again for three minutes, etc.
Use the keyboard to enter a real number t that represents the number of minutes that have elapsed since the beginning of the hour.
Determine what color the traffic light is at the specified time.
Display the result as follows:
"green" if the light is green,
"yellow" if the light is yellow, and
"red" if the light is red.

Example for 2.5:
green
Example for 3:
yellow
Example for 4:
red
Example for 5:
green

Requirements:

The program should read a real number from the keyboard.
The program should display text on the screen.
If the light is green, display: "green"
If the light is yellow, display: "yellow"
If the light is red, display: "red"

package com.codegym.task.task04.task0416; import java.io.*; public class Solution { public static void main(String[] args) throws Exception { BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); String input1 = reader.readLine(); double a = Double.parseDouble(input1); if(a >= 0 && a < 1) { System.out.print("green"); } else if(a % 4 >= 0 && a % 4 < 1) { System.out.print("red"); } else if(++a % 4 >= 0 && a % 4 < 1) { System.out.print("yellow"); } else { System.out.print("green"); } } }

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Gellert Varga

Level 23 , Szekesfehervar, Hungary

6 February 2021, 18:43

This is the system: 0 - 3 min. = green 3 - 4 min. = yellow 4 - 5 = red. The cycle starts again: 5 - 8 = green 8 - 9 = yellow 9 - 10 = red. The cycle starts again: 10 - 13 = green 13 - 14 = yellow 14 -15 = red. etc, etc. Look it more closer, one lamp-cycle lasts how many minutes! 4 ? Test your program for example with input 8.5 and 13.5. Both of these need to return yellow (see above). But your program returns some other values.