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#lang racket
(define/contract (dest-city paths)
(-> (listof (listof string?)) string?)
(define city-pairs (make-hash paths))
(define (go-to-next-city origin)
(let ([destination (hash-ref city-pairs origin #false)])
(if destination
(go-to-next-city (car destination))
origin)))
(go-to-next-city (caar paths)))
(dest-city '(("London" "New York")
("New York" "Lima")
("Lima" "Sao Paolo")))
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