501: Connect the first two images. Third image (of the group) can act as a clue.

500: The so called “Night of Shame” monument at Bebelplatz, Berlin. The Bebelplatz is best known as the site of the book burning ceremony held on May 10, 1933 by members of the S.A. (“brownshirts”) and Nazi youth groups, on the instigation of the Propaganda Minister, Joseph Goebbels. The Nazis burned around 20,000 books, including works by Thomas Mann, Erich Maria Remarque, Heinrich Heine, Karl Marx and many other authors. Today a glass plate set into the Bebelplatz, giving a view of empty bookcases, commemorates the book burning. Furthermore, a line of Heinrich Heine is engraved, stating “Dort, wo man Bücher verbrennt, verbrennt man am Ende auch Menschen” (in English: “Where they burn books, they ultimately burn people”).