Have Row & Column Number, and Sheet Name - Get Value

Cell A1 = Row Number
Cell A2 = Column Number
Cell A3 = Sheet Name

How do I add all of these together to get the value from a cell as you would with:

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I'm sure this is so simple but there you go!

Thanks
dvent

You can use INDIRECT in either of the below forms

=INDIRECT("'"&A3&"'!R"&A1&"C"&A2,FALSE)

or

=INDIRECT(ADDRESS(A1,A2,,,A3))