What is the highest overall pick that has c as the position, with an NFL Draft greater than 1977?
CREATE TABLE "top_nfl_draft_selections" (
  "player" text,
  "position" text,
  "overall_pick" real,
  "round" text,
  "nfl_draft" real,
  "franchise" text
);
SELECT MAX("overall_pick") FROM "top_nfl_draft_selections" WHERE "position"='c' AND "nfl_draft">1977;