Suppose $z=f(x,y)=\sqrt[\phantom{2}]{x-y},$ where $x=x(t)$ and $y=y(t).$ If $x(1)=2,y(1)=-2,x^{\text{'}}(1)=4$ and $y^{\text{'}}(1)=16,$ find $\frac{dz}{dt}(1).$ Enter your answer in the answer box below without spaces.

$\frac{dz}{dt}(1)=$