Name the duration for georgi grechko
CREATE TABLE "expeditions" (
  "expedition" text,
  "crew" text,
  "launch_date" text,
  "flight_up" text,
  "landing_date" text,
  "flight_down" text,
  "duration_days" text
);
SELECT "duration_days" FROM "expeditions" WHERE "crew"='Georgi Grechko';