During which stage was the Intergiro classification held by Miguel Indurain, the Points classification held by Mario Cipollini, and the Young rider classification held by Leonardo Sierra?
CREATE TABLE "classification_leadership_by_stage" (
  "stage" text,
  "winner" text,
  "general_classification" text,
  "points_classification" text,
  "mountains_classification" text,
  "young_rider_classification" text,
  "intergiro_classification" text,
  "trofeo_fast_team" text
);
SELECT "stage" FROM "classification_leadership_by_stage" WHERE "intergiro_classification"='miguel indurain' AND "points_classification"='mario cipollini' AND "young_rider_classification"='leonardo sierra';