Compare cell values and display negative or positive value?

New to LibreOffice calc and its a big program =).
Lets imagine I have cells looking like this below. In C column I want to add values of difference from previous value in B column

A                 B         C
2019-01-02       500
2019-01-03       700
2019-01-04       200
2019-01-05       800

So it look s something like this -

A                 B         C
2019-01-02       500   
2019-01-03       700       200
2019-01-04       200      -500
2019-01-05       800       600

How to achive this the smartest way?

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With me Windows 10 Home; Version 1809; 64-Bit | LibreOffice, Version: (x64)…

With greatest gratitude I thank you´for your answer and helping me out.
Danke Schön!

Always my pleasure.