Script to create and name subfolder from selected files in Bridge

I have re-purposed some code I found on this forum for creating a subfolder automagically but there is one little tidbit I cannot figure out how to code correctly.

The goal is to grab a selection of RAW images, and create a folder with the name of the first image selected and move the images into it. I have functional code that does all of that, but I cannot figure out how to grab the name of the first file for the folder name. I have band-aided the code to ask for a name, but I am hoping that there is an easy solution for grabbing the first file name.

#target bridge

if(BridgeTalk.appName == 'bridge'){

selItems = MenuElement.create('command', 'Move DSC Images', 'at the end of Thumbnail');

}

selItems.onSelect = function(){

try{

var thumbs = app.document.selections;
var a = 0;

if(thumbs.length < 1) return;

var firstFile = prompt("Last 4 digits of first file name") ;
if (firstFile== undefined) {return};

var newFolder = new Folder(app.document.presentationPath+"/"+'DSC_'+firstFile+"/");

if(!newFolder.exists) newFolder.create();

var foldT = new Thumbnail (newFolder);

app.synchronousMode = true;

for(a = 0; a < thumbs.length; a++){

if(thumbs[a].parent != foldT){

var copyFile = File(newFolder.fsName + '/' + thumbs[a].name);

if(!copyFile.exists){

thumbs[a].moveTo(newFolder);

}

else{

var j = 1;

while(copyFile.exists){

var nSplit = thumbs[a].name.split('.');

ext = nSplit.pop();

thumbs[a].name = nSplit.join('.') + ' (' + j + ')' + '.' + ext;

copyFile = File(newFolder.fsName + '/' + thumbs[a].name);

j = j + 1;

}

thumbs[a].moveTo(newFolder);

}

}

}

app.synchronousMode = true;

app.document.chooseMenuItem('Refresh');

}

catch(e){

alert(e + e.line);

}

}