How could I convert the y axis in a Vector 3 into a float?

Here's my script :

 #pragma strict
 
 var forwardSpeed : float = 20;
 var leftRotate : float = 5;
 var rightRotate : float = 5;
 var upLift : Vector3;
 var number : float = 0;
 
 function Update () {
 
 upLift = transform.InverseTransformDirection(rigidbody.velocity);
   
 if (Input.GetKey(KeyCode.Space)) {
 
     rigidbody.AddForce (transform.forward * forwardSpeed);
 
 }
 
 
 }

So I want the y axis of upLift to be turned into a float and used in the variable "number"