I try to say hi to my crush everyday and some days she say hi back and some days she just smiles?

I have a huge crush on this girl at work. Haven't had the opportunity to ask her out as she works in a different department. When i see her in the hallways i try to say hi to her and sometimes she says hi back or she just smiles. Does it mean anything or could she just be being friendly?
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Also, i usually don't say hi to random girls but she did smile at me once before i started saying hi to her.
I try to say hi to my crush everyday and some days she say hi back and some days she just smiles?
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