#define F_CPU 16000000UL
#define __AVR_ATmega328P__
#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);
  }
}