When the area was disputed between Weimar Germany and the Second Polish Republic, the Poles recalled the massacre quoting the number of 10,000 murdered. After Nazi Germany had annexed the Free City of Danzig in World War II, the exiled Polish government in releases said that the knights had "massacre ten thousand souls", portrayed the contemporary Germans in the tradition of these events and linked these events with National Socialism. In 1969 the post-war Polish city authorities dedicated a monument that commemorates the massacre of the population of Gdańsk in 1308. Its stated aim was to propagate an analogy of the events of 1308 and the German crimes of World War II. On the monument, called Tym co za Polskość Gdańska , the dates 1308, 1454, 1466 and 1939 are mentioned, relating the events of 1308 to the Thirteen Years' War and World War II.
Question: How many years after the population of Gdańsk was massacred did Polish city authorities dedicate a monument commemorating those killed?
Answer: 661