Hi every body

i am trying to lookup a unique value in 6 different workbooks, i tried the
following argument,
=IF(ISNA(VLOOKUP($A:$A, Sheet2!$A:$B, 2, FALSE)), VLOOKUP($A:$A,
Sheet3!$A:$B, 2, FALSE), VLOOKUP($A:$A, Sheet2!$A:$B, 2, FALSE)),
but it works with two different workbooks/sheets, but i have 6 different
workbooks,

pleaaaaaaaaaze help of think to use some thing else to get same result

i tried to put AND/OR, but i failed to get it work.
thanks