how do i add (Vertical) to context in untiy 4 its telling me its a compiler error

using UnityEngine;
using System.Collections;

public class NewBehaviourScript : MonoBehaviour {

// Use this for initialization
void Start () {

}

// Update is called once per frame
void Update () {
                                                
	float forwardSpeed = Input.GetAxis (Vertical);

	Vector3 speed = new Vector3 (0, 0, forwardSpeed);

	CharacterController cc = GetComponent<CharacterController>();

	cc.SimpleMove ( speed );
}

}

Try putting Vertical in quotes: “Vertical”