`
cost=0 
    flag=0 
    if bc+z<wc:
        flag=1
        cost=cost+(bc+z)*w
    if wc+z<bc:
        flag=2
        cost=cost+(wc+z)*b
    if flag==0:
        cost=(bc*b)+(wc*w)
    if flag==1:
        cost=cost+(b*bc)
    if flag==2:
        cost=cost+(w*wc)
    return cost