Appending to the Access DB from c#

Question

I have c# app which should append rows to MS Access table.
That table is basically a composition of 3 tables (let's say they all have a single column
Table1 with column A, Table2 - column B, Table3 - column C
Query - INSERT INTO Table4 (SELECT A, B, C FROM Table1, Table2, Table3)
Obviously it runs ok only for first time only and generates "Duplicate records" error after that.
It's easy to handle within Access but not from c# code.
What do I do, so it only appends a new rows and ignores duplicates without writing a long code?