Task: Question Generation
Input (English): Passage: The conflict between Novgorod and Teutonic Knights began in 1210, when the knights attacked the Estonians. Novgorod campaigned against the Livonians in 1217, 1219, 1222, and 1223, facing repeated failure. In 1224, the knights captured Dorpat . Soon after the capture of Dorpat, an internal conflict arose in Novgorod. The townspeople refused to help in the fight against the knights. Soon, a split occurred among the Novgorod nobles. Expelled from the city, the nobles and the Knights captured Izborsk in 1233, but soon were expelled from the city by the Pskov army. A year later, Yaroslav Vsevolodovich of Novgorod returned to the Livonian lands and devastated the outskirts of the town Odenpa, triumphing over Emajõe and forcing the Livonians to sign a peace agreement. In 1236, Lithuania had lost a Great Master of the Order of the Sword Volquin von Winterstein, and Pope Gregory IX gave his consent to the Union of the Order of the Sword with the Teutonic Knights. The master of the Order was Hermann von Balk. In December 1237, Pope Gregory IX proclaimed the second crusade against Finland. Danish king Waldemar II and the joint Masters of the Order agreed to divide Estonia and attacked Baltic Russia in June 1238 in collaboration with the Swedes. The Russian lands were weakened by the Mongol invasion.
Output (English): How many months after the second crusade was proclaimed did the Danish attack Baltic Russia?