As KSSV shows, the proper way to build a path containing the folder and name of a file you want to import is with fullfile, and if you want to continue to use input, I recommend you accept his answer.
Note that as per Steven's comment, you should not be manipulating matlab's path. All the file IO functions can work directly with the full path of the file and the file doesn't have to be on the matlab path (and actually shouldn't be, separate data from code). So pass the path directly to xlsread.
However, forcing the user to paste a path is not a very good UI. That forces them to go outside of your interface to find the file, copy the path, go back to your UI, and paste it. Not very user friendly.
Instead you can let them do that easily from your interface by using uigetfile. As a bonus, you're guaranteed that the path you receive is valid (or that the user cancelled the selection):
[filename, filepath] = uigetfile('*.xls;*.xlsx', 'Select Exel data file');
if isequal(filename, 0)
error('User cancelled file section')
[num, txt, raw] = xlsread(fullfile(filepath, filename));