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In most places only the " first " wall is marked , except near Potsdamer Platz where the stretch of both walls is marked , giving visitors an impression of the dimension of the barrier system .
 Potsdamer Platz
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Potsdamer Platz