undefined function or variable 'N'

why do i get the error in the title. I also tried iteration(n), the file is named the same aswell and I cant seem t get past the error message.

function iteration
%   Summary of this function goes here
%   Detailed explanation goes here

% Sum variable put to 0
S = 0;

% Input n
n = input('Please give the nuber of iterations: ');

%the sum is constructed
for k=0:n
    S=S+(1+(4/(S+1)));
end

end

Answer 1

[KSSV]

function S = iteration(n)
%   Summary of this function goes here
%   Detailed explanation goes here
% Sum variable put to 0
S = 0 ;
%the sum is constructed
for k=0:n
    S=S+(1+(4/(S+1)));
end
end

Now call it by:

n = 10 ;
S = iteration(n) ;