What was the Stage when Pascal Richard had the Mountains classification and Vladimir Poulnikov won?
CREATE TABLE "classification_leadership_by_stage" (
  "stage" text,
  "winner" text,
  "general_classification" text,
  "points_classification" text,
  "mountains_classification" text,
  "young_rider_classification" text,
  "trofeo_fast_team" text
);
SELECT "stage" FROM "classification_leadership_by_stage" WHERE "mountains_classification"='pascal richard' AND "winner"='vladimir poulnikov';