Compounding two conditional functions of x

Hello,

Is it possible to combine the following functions into one?

x := 0.5m

ft(z) := if(z<=x, f(z), f(x)+f2(z-x))

f(z) := 850*g*z

f2(z) := 1024*g*z

ft(z) calculates the static pressure at depth z in a 0.5m layer of oil on top of water. So if z is in the oil the result is just f(z), but if in the water layer, f(0.5)+f2(z-x).

My fluids lecturer hinted that this kind of problem can be solved without the use of ifs, but didnt seem eager to expand!

I'm wondering if it can be solved through knowledge of the pressure-depth gradients of each fluid... but it's mirky!