What is the logic when we make copy of copy

Question

What is the logic when we make copy of copy file in any  windows operating system.

 

Suppos i have file ABC.txt

now I Copy this and pasete into same folder. this name willl be ABC.txt -copy

now i ll copy again of ABC.txt then this name will be ABC.txt -copy(2)

 

What is the logic behind .I need this requirement in C# code please reply if any body knows?