join command

All,
I have 3 files (tab seperated):

Note: Please treat dash (-) as empty value in the file, I have added it to make input easily readable

file1: (2 cols)
A 1
B 2
C 3

file2: (4 cols - col4 has empty values for 4th column except 2nd row)
A 1 5 -
B 2 6 Y
C 3 7 -
D 4 8 -

file3 (2 cols):
A 5
C 7

And the output of file1, file2, file3 merged together like:

A 1 A 1 5 - A 5
B 2 B 2 6 Y - -
C 3 C 3 7 - C 7

    • D 4 8 - - -

Can someone hint any unix command or little shell script that would help me do it? I am trying to use *join* but is getting tricky.

Thanks in advance,
MK.

paste file1 file2 file3