What did I do wrong?

I am trying to solve the second question which is k in the given model, what did I do wrong?

function [tv, uv] = RK4(f, u0, T, n)
dt = T/n; % Differential of time.
tv = transpose(0:dt:T); % Evaluation times.
uv = zeros(n+1, 1); % Solution.

uv(1) = u0; % Initial value
for i=1:length(tv)-1
    k1 = f(tv(i), uv(i))
    k2 = f(tv(i) + (dt/2), uv(i) + dt*k1/2)
    k3 = f(tv(i) + (dt/2), uv(i) + dt*k2/2)
    k4 = f(tv(i) + dt, uv(i) + dt*k3)
    uv(i+1) = uv(i) + dt/6*[k1+2*k2+2*k3+k4]
end
end

u0 = 5000; 
lambda = 0.03;
pm = 9000;
f = @(t,k) lambda*500*(1-500/pm)-k;
[t,k] = RK4(f,u0,100,10)
Kf = k(end)