Task: Question Generation
Input (English): Passage: The Koreans waited until a large Japanese fleet had left the island for a raid. Yi Jong-mu's fleet of 227 ships and 17,285 soldiers set off from Geoje Island toward Tsushima on June 19, 1419. The following day the fleet landed in Asō Bay . General Yi Jong-mu first sent captured Japanese pirates as emissaries to ask for surrender. When he received no reply, he  sent out expeditionary forces, and the soldiers proceeded to raid the islanders and pirates and plunder pirate settlements. He found and rescued 131 Chinese captives of the pirates and 21 slaves on the island, burned 129 ships and 1,939 houses, and killed or captured 135 pirates. On the 26th day, the Korean army was ambushed on land by a Japanese army in an ambush at Nii, and suffered 150 casualties. The ambush was known to the locals as the Battle of Nukadake . In the weeks that followed, a truce was negotiated with the Sō clan on the island. The Korean expeditionary force withdrew and sailed back to the Korean Peninsula on July 3, 1419. and Korea gave up occupation of Tsushima. In subsequent diplomatic exchanges, Tsushima would be granted trading priveldges with Joseon, in exchange for maintaining control and order of pirate threats originating from the island.
Output (English): How many days after landing was the Korean army ambushed by the Japanese?