Indexing multiple columns to return a result from a separate column

Please help me with this one:

Sheet2:
col A = contains the style#
col B = contains the color of the style
col C = contains the size of the style
col D = contains the qty of the style,color, size

Sheet1:

I would like to do the following:

A1 = input the style #
B1 = input the color of that style
C1 = input the size of that style

then D1 should automatically contain the qty of the mentioned style, color, and size.

Please help. Thank you.

Try

=Sumproduct(--(Sheet2!A1:A100=A1),--(Sheet2!B1:B100=B1),--(Sheet2!C1:C100=C1),D1:D100)

adjust ranges/references to suit.