Simple C#/ASP.Net Modification

Right now I have a line of code that has a hardcoded value. I want to have a message box pop up and ask for the value, and then select the file based upon the number entered. Due to the simple nature of this and the 4GB file size, the coder will be required to work directly on my machine using teamviewer(which is free), or I can upload the .cs file you will need, but would prefer to have you edit directly on the system so I can explain something if necessary. I will show you directly on the system before you bid if you would like<--- This isn't more than 20 minutes worth of work, preference goes to those who can complete this immediately <-------------- Example I have a line of code that says Load([login to view URL] + "[login to view URL]") Message Box pops up and asks for Code User Enters 1 The line will go into that folder and input the file name in the line so now it would be Load([login to view URL] + "[login to view URL]") User Enters 2 so now it would be Load([login to view URL] + "[login to view URL]") if the user enters an invalid number(doesnt exist in folder) it should indicate it doesnt exist. That Simple!