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How do I connect to a pc through another pc using ssh

How to go about doing in one command line the following operations?

$ ssh server-one
$ su - user
$ ssh server-two

Of course I cannot directly ssh user@server-two

ssh server-one -t ssh user@localhost -t ssh server-two

From man ssh:

     -t      Force pseudo-tty allocation.  This can be 
             used to execute arbitrary screen-based programs 
             on a remote machine, which can be very useful, 
             e.g. when implementing menu services.  Multiple -t
             options force tty allocation, even if ssh has no local tty.
ssh -t server-one 'su - user -c "ssh server-two"'

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