Click to Move without using objects

Hello, I am trying to make a click to move script that finds the mouse position and moves the player to it. However, it gives this error:

    Assets/NewBehaviourScript.js(13,62): BCE0077: It is not possible to invoke an expression of type 'UnityEngine.Vector3'.

And my code is:

#pragma strict

var cam = Camera.main;
var clickPosition = Vector3.zero;

function Start () {

}

function Update () {
	if(Input.GetKeyDown(KeyCode.Mouse0))
	{
		clickPosition = cam.ScreenToWorldPoint(Input.mousePosition());
		clickPosition.z = 0;
		Debug.Log (clickPosition);

    	
	}
}

Thanks in advance.

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