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# [Brain-Flak], 12 bytes

    {({}<>)<>}<>

[Try it online!][TIO-kjgtjwwz]

[Brain-Flak]: https://github.com/DJMcMayhem/Brain-Flak
[TIO-kjgtjwwz]: https://tio.run/##SypKzMzTTctJzP7/v1qjutbGTtPGDkj@/1@cmJKTlp2VWJxi/V83GQA "Brain-Flak – Try It Online"

    # (Implicitly) Read characters from STDIN and place them all on the active stack
    
    # While the top of the active stack is not null...
    {
        # Push the following value on to the active stack
        (
            # Pop the current character off the active stack and add it to the value we're tracking
            {}
            
            # Toggle which stack is active
            <>
        # (push)
        )
    
        # Toggle back to the stack the input was on
        <>
    
    # (endwhile)
    }
    
    # Toggle stacks back so that the secondary stack is active when the program ends
    <>
    
    # (Implicitly) Print all values on the active stack