uigetfile - limit of files which can be loaded

How to improve number of files which can be loaded with uigetfile command

This script I use to improve the contrast of images by using imadjust command. The only problem is limited number of files (about 40 - 50) which can be processed at once.
The code is:

function autocontrast

warning off
clc;
clear all;

%--------------------------------------------------------------------------
[FileName,PathName] = uigetfile('*.tiff','Select any image', 'MultiSelect', 'on');

if PathName~=0;
n= length (FileName)

for a=1 : 1: n
input_image=imread([PathName,FileName{a}]);

I_imadjust = imadjust(input_image);
%figure, imshow(input_image_imadjust);
%----------------------------------------------------------------------
mkdir(PathName,'imadjust')
FN1= fullfile(PathName,'imadjust',FileName{a});
imwrite(I_imadjust,FN1);

end
end