Head Look for Mecanim

I have following script, how can i find position of mouse to look at? I wan’t to make a script like Mouse Look in Standard Assets FPS, but for Mecanim.

using UnityEngine;
using System.Collections;

public class HeadLook : MonoBehaviour {
	Animator animator;
	void OnAnimatorIK (){
		Vector3 target = ???
		animator.SetLookAtPosition (target);
	void Start ()

That depends on what you want to look at. If you want to look at an object, you could use

public Transform target;

And set in the inspector a target object. Then:

Vector3 target_look_position = target.position;

Or you could just hard code a vector3.

Vector3 target_look_position = Vector3(0, 0, 0);