Pythagorean equation in Max

Augustine Bannatyne - Leudar's icon

Can someone show me how to do the follwing equation in expr object :

whereby the X,Y,Z are $1s and I get the "PQ" as an output. Im basically trying to get the distance between two moving ponts in 3D space
thanks

Floating Point's icon

expr sqrt($f1*$f1+$f2*$f2+$f3*$f3)