Upon receiving a MAYDAY distress call from an aircraft on frequency, what is the immediate primary duty of the controller under ICAO Doc 4444?

1. Immediately acknowledge the distress call, clear the frequency of non-essential traffic, and take control action to assist the aircraft
2. Instruct the aircraft to switch to an unmonitored secondary frequency to avoid disturbing other traffic
3. Request the pilot to complete a written distress form before providing vectors
4. Hand off the aircraft to an adjacent FIR immediately without issuing assistance