Task: Question Understanding
Input (English): Passage: Before the UNPROFOR fully deployed, the HV clashed with an armed force of the RSK in the village of Nos Kalik, located in a pink zone near Šibenik, and captured the village at 4:45 p.m. on 2 March 1992. The JNA formed a battlegroup to counterattack the next day. The JNA battlegroup, augmented by elements of the 9th Military Police Battalion, deployed at 5:50 a.m. and clashed with the HV force in Nos Kalik. However, the JNA counterattack failed. The HV captured 21 RSK troops in Nos Kalik, intent on exchanging the prisoners for Croats held under arrest in Knin. Following negotiations, the HV agreed to pull back on 11 April, but later declined to do so, claiming deteriorating security at the battlefield in general prevented the withdrawal. Several Serb-owned houses in Nos Kalik were torched after the HV captured the village. The HV clashed with units subordinated to the 180th Motorised Brigade of the JNA in a pink zone near Zadar on 17-22 May. While the JNA repelled attacks in most areas around Zadar and Stankovci, the HV managed to cut a JNA base at the Križ Hill away from the rest of the force on 17 May. The JNA outpost occupied high ground overlooking the surrounding area, including Zadar. It housed radar equipment and was used as an artillery observer post. The JNA attempted to relieve the besieged garrison in the next few days, however the attempts failed and the base surrendered to the HV on 22 May. The attack and capture of the Križ Hill, codenamed Operation Jaguar, was carried out by the 2nd Battalion of the 159th Infantry Brigade of the HV, supported by artillery of the 112th Infantry Brigade.
Question: How many days after the village of Nos Kalik was captured did HV agree to pull back after negotiations?
Output (English): number