Lerp Issue

var endPosition : Vector3 =Vector3 (0.0, 0.5, -5);
var lerpSpeed : float = 0.1;
private var startPosition : Vector3;
private var startTime : float;

function Start () {
	startPosition = transform.position;
	startTime = Time.time;

}

function Update () {
	transform.position = Vector3.Lerp(startPosition, endPosition, lerpSpeed * Time.time - startTime);
}