got stuck in equation

[usamazohad at gmail.com]

hi . . my name is usama khan 
i am the student of civil engeering  and we got assignment to make a project program on flexible pavement design using python.
 
i know very litle about programing. still learning from tutorials. u can call me a beginner.
now i need to solve this equation so that i can put this in python but the formula of design is very complex 
 
Formula is :
 
log(W18) = (Z)(S)+9.36log(SN+1) -2.0+(log(dpsi/(4.5-1.5))(/(.40+1094/(SN+1)^2.5)+2.32log(Mr-)-8.07
 
every thing is constant except this SN. . i want to seperate SN like SN= rest of the stuff. how can i seprate it because manualy its impossible to take SN out.
so plz help me out