Plot V-S plot of Enzyme Activity by Euler Algorithm

    I need help regarding an assignment question on enzyme kinetics
Stimulate V-S plot of enzyme activity from the equation :- 
ds/dt =-Vm*s/(Km+s).
use Euler's algorithm. 
use Vm=5 Km=200 Assume that the simulation will run for 200s at the time interval of 0.1. Initial value of S being 100
I am trying the following script

S=input('enter substrate concentration') V=input('enter velocity') V=0; Km=input('enter michaelis-menten constant') Km=0; tmax=input('maximum time'); tau=input('minimum interval'); S(1)=1; T(1)=1; for i=1:S S(1+S)=S(100)*(Km+S); T(1+S)=-T(1)*V*S; end

 plot(V,S)   
    and then saving as enzyme.mat
but it is showing the following error

Attempted to access S(100); index out of bounds because numel(S)=1.

Error in enzyme2 (line 11) S(1+S)=S(100)*(Km+S); please explain me the corrections Thank you