Logic Gates!

What is the minimum number of basic one/two input gates needed to implement the following Boolean Function?

$F(w, x, y, z) = w'x'y'z' + wx'yz' + x'y'z' + w'x'z' + wxz + xy'z + w'xz$

Clarifications:

• Basic Gates include AND, OR, and NOT only. XOR, NAND and NOR gates do not count in this problem.
• Each AND/OR gate must only accept two inputs. Each NOT gate must only have one output.
• Available inputs are only w, x, y, and z.

As an explicit example,

For the function $F (x,y,z) = xy'z + xy'z' + x'y'$ , this can be simplified to be $F (x,y,z) = y'$ , which means it only needs one NOT gate to have the function implemented.