input instead of range

[kenpcli]

I have a line of code that was looking at the beginning and ending spreadsheets, but now they are adding more spreadsheets so instead of certain sheets defined I would like it to pop up a input box. Here is the code I have currently:

"=IF(ISNA(VLOOKUP(C2,'12-31 TO 01-06'!$C$1:$E$500,2,FALSE)),""NONE"",VLOOKUP(C2,'01-07 TO 01-13'!$C$1:$E$500,2,FALSE))"

Thank you