I used annotation because accepts normalised units, otherwise text might be a better option. Have a look at it.
Also I stronlgy suggest you to avoid naming variables with function names, such as length.
Finally, unless needed for demonstration purposes, avoid live scripts and use normal scripts.
By doing so you can initialise a figure outside the loop, instead of setting the same figure title at each iteration with title('dynamic graph'); inside the loop.
for i=1:length %ciclo for 200 giri
in=circshift(in,1);
in(1)=seq(i);
ff = sum(in.*variable_f);
if i>n
e = ff - seq(i-n);
variable_f= variable_f - step*e*conj(in);
end
plot(variable_f)
% Command to show current iteration (add this to your loop):
iteration = annotation('textbox', [.7 .7 .1 .1], ...
'EdgeColor', 'None', ...
'String', [num2str(i) '/' num2str(length)], ...
'FontSize',20);
drawnow
title('dynamic graph');
end