In order to specify the complete file path you will have to type in the absolute file path.
The absolute file path will be passed to loadtxt command as an argument
In order to understand the file path of your desired file, use the Windows explorer/File explorer and navigate to the where the file is located, Right click on the file, Open Properties and you will find the complete file path specified there.
Here also you can use the File explorer to find the exact file path of your file.
In case you are still facing an issue, kindly paste the traceback here and we can help.