From 17-20 July the Hungarian army bombarded the Romanian positions and conducted reconnaissance operations. On 20 July at about 3:00 am, after a fierce bombardment, Hungarian infantry including all three groups crossed the Tisza River and attacked Romanian positions. On 20 July, in the northern arena, the Hungarians army Rakamaz and some nearby villages. Troops of the Romanian 16th and 2nd Vanatori divisions took back the villages shortly and regained Rakamaz the next day. The Hungarians renewed their efforts and, supported by artillery fire, retook Rakamaz and two nearby villages but could not break out of the Rakamaz bridgehead. Hungarian forces attempted to outflank the Romanian positions by crossing the Tisza River at Tiszafured with troops of the 80th International Brigade. There they were halted by troops of the Romanian 16th Division. On 24 July the Romanian 20th Infantry Division, brought in as reinforcements, cleared the bridgehead at Tiszafured. Not being able to break out of Rakamaz, Hungarian forces fortified their positions and redeployed some troops. There was a lull in fighting in the north, as the Romanian troops did the same. On 26 July the Romanians attacked, and by 10:00 pm had cleared the Rakamaz bridgehead. This left the Romanian army in control of the northern part of the Tisza's eastern bank.
Answer this question: How many days after they started their bombardment did the Hungarian army cross the Tisza River?
3