#define F_CPU 16000000UL
#include <avr/io.h>
#include <util/delay.h>


int main(void)
{
   DDRB = 0xff;

    while (1) 
    {
        // green
        PORTB |= (1<<PORTB5);
        _delay_ms(500);
        PORTB &= ~(1<<PORTB5);

        // yellow
        PORTB |= (1<<PORTB4);
        _delay_ms(500);
        PORTB &= ~(1<<PORTB4);

        // red
        PORTB |= (1<<PORTB3);
        _delay_ms(500);
        PORTB &= ~(1<<PORTB3);

        // red and yellow
        PORTB |= (1<<PORTB3);
        PORTB |= (1<<PORTB4);
        _delay_ms(500);
        PORTB &= ~(1<<PORTB3);
        PORTB &= ~(1<<PORTB4);
    }
}