user: Question: Who was the lead envoy of the Congratulation mission in 1718 with the Ryūkyūan King Shō Kei?
Columns: ['Year', 'Mission type', 'Shogun', 'Ryūkyūan King', 'Lead Envoy', 'Number in entourage']
Types: ['real', 'text', 'text', 'text', 'text', 'text']
Sample row: [1634.0, 'Congratulation & Gratitude', 'Tokugawa Iemitsu', 'Shō Hō', 'Princes Tamagusuku, Kin, Sashiki', 'Unknown']
SQL:

assistant: SELECT "Lead Envoy" FROM "Table" WHERE "Ryūkyūan King" = 'Shō Kei' AND "Mission type" = 'Congratulation' AND "Year" = 1718.0;