k*b + k*s - s - k
k*b + k*s - s - k при k = -4
(-4)*b + (-4)*s - s - (-4)
-4*b - 4*s - s - (-4)
4 - 5*s - 4*b
-k - s + b*k + k*s
-k - s + k*(b + s)
-k - s + k*b + k*s