After repelling the Hungarian attack, the Romanian army prepared to cross the Tisza River. The 7th Infantry Division returned from Bessarabia. The 2nd Infantry Division and some smaller infantry and artillery units also returned. The Romanian army massed 119 battalions , 99 artillery batteries with 392 guns and 60 cavalry squadrons . Hungarian forces continued an artillery bombardment. From 27-29 July the Romanian army tested the strength of the Hungarian defense with small attacks. A plan was made to cross the Tisza River near Fegyvernek, where it makes a turn. At the night of 29-30 July the Romanian army crossed the Tisza River. Decoy operations were mounted at other points along the river, bringing intense artillery duels. Romanian forces held the element of surprise. On 31 July the Hungarian army retreated towards Budapest.
Question: How many days after the Romanian army crossed the Tisza River did the Hungarian army retreat towards Budapest?
Answer: 2