You have defined your function handle as -
f = @(t,y,s,r,Nddotmax) (r*((1-y)/Nddotmax)+s-0.0012*0.02*y);
Which means it requires 5 inputs to give you an output. Though 't' isn't mentioned in the expression, so either remove it or check the expression again.
But you are only calling it with 3 inputs, that is why it is giving the error
yprime=y(i)+h*f(t(i),y(i),s(i)); %slope
y(i+1)=y(i)+h*f(t(i+1),yprime,s(i+1))
To fix the problem, call your function handle with 5 input.
Also, defining syms variable is redundant as you are using a function handle.