I have multiple subdirectories inside a directory and each of them contains a file with the same name (but different contents). I wish to copy all these files of the same name into a destination directory such that they each have a unique name. The unique names can be differentiated with timestamp, or the directory name can be appended to each file name.
Example:

File 1: A/abc.txt  
File 2: B/abc.txt  
File 3: C/abc.txt

The destination folder is R, and it should result in something like this after the copy:

R: A_abc.txt   B_abc.txt   C_abc.txt

I have tried several variations of the following command but cannot seem to get to the required output:

find . -maxdepth 2 -name '*.txt' -exec cp {} ../R/ ;

Please suggest an approach.