What is the mandatory action required by an octagonal red sign with white 'STOP' lettering (Znak II-2, 'Obavezno zaustavljanje')?

1. Bring the vehicle to a complete standstill at the stop line (or intersection edge) and yield to all cross-traffic
2. Slow down and roll through without stopping if no other vehicles are visible
3. Stop only if approaching traffic from the right is closer than 50 metres
4. Stop only when an oncoming vehicle flashes its headlights