What is the minimum number of NAND gates needed for the below given?
\(f\left( {X,Y,Z,W} \right)\; = X\bar YZ\bar W + \bar X\bar Y\bar Z\bar W + X\bar Y\bar Z\bar W + \bar X\bar YZ\bar W + \;\bar XY\bar ZW + \bar XYZW + \;XY\bar ZW + XYZW\)
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