function main() {
	app.beginUndoGroup("rename"); // so we can revert it
	var curComp = app.project.activeItem; // get the active item
	// do a check if the item is a comp
	if (!curComp || !(curComp instanceof CompItem)) {
		alert("this is not a comp");
		return;
	}
	// get a name from the user
	var name = prompt("Please enter a new name", "new-name", "Add a name");
	// do a check if the user entered something
	if (name.length === 0) {
		alert("no name provided");
		return;
	}
	// loop the selected layers
	for (var i = 0; i < curComp.selectedLayers.length; i++) {
		var layer = curComp.selectedLayers[i];
		layer.name = name + " " + i;
	}
	app.endUndoGroup();
}
main(); // call the function

var doc = app.activeDocument;
for (var i = 0; i < doc.layers.length; i++) {
	var layer = doc.layers[i];
	layer.name = "Layer\_" + i;
}