def Series(R1, R2):
   Rnet = R1 + R2
   return(Rnet)

def Parallel(R1, R2):
   Rnet = 1 / (1/R1 + 1/R2)
   return(Rnet)

def Circuit(R):
    Ra = Series(R,200)
    Rb = Parallel(Ra, 450)
    Rc = Series(Rb, 75)
    Rd = Parallel(Rc, 250)
    Rab = Series(Rd, 50)
    return(Rab)

for R in range(100,400,100):
    Rab = Circuit(R)
    print('R = ',R,' Rab = ', Rab)