x=0.2;
c=0;

% f=@(x) 0.4*x*(1-x);
f=@(x) x*(1-x);


for k=1:500000
    xnew=f(x);
    if abs(xnew-c)<10^(-5)
        fprintf('Number of iterations: %d\n',k);
        break
    end
    x=xnew;
end