Read NFC tags and back button

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http://stackoverflow.com – My problem is related to the back button and the backstack, ive got a app for reading nfc tags, so ive launch Activity A, then go for Activity B, that is declared SingleTop in the manifest. I aproach the phone to the tags and it reads the tag, everything is working fine at this moment. If i press the back button , it goes back to activity B,instead of going to the Activity A, and then if i pressed the backbutton again it goes to Activity A. Like this: A->B->read Tags->B->press back button ->B->press back button ->A->press back button ->close app. and i want like this: A->B->read Tags->B- (HowTos)