how to discard the same textbox value

i have a textbox which containsa a value==
Bangkok/Bangkok-Ayutthaya-Khao Yai National Park(B)/Khao Yai- Sukhothai(B)/Sukhothai-Phitsanulok(B)/Phitsanulok-Bangkok/Bangkok[Departure]
 
i want to discard the same values in this textbox like bangkok occur 4 times sukhothai occur 2 times. these value can seen just one time.
 
i want it will change into
Bangkok/Ayutthaya/Khao Yai national Park/Shukhothai/Phitsanulok
 
how to do this...............
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