GetKeyDown sound error

Hi, So I tried to make it when I press the ‘‘F’’ it plays a sound. I have this javascript:

var audio01 : AudioClip;


function Update () {   
    if (Input.GetKeydown  (KeyCode.F))
   {
      audio.PlayOneShot(audio01);
 
   }
}

But when I try it, it doesn’t play the sound, or I get this error: MissingMethodException: UnityEngine.Input.GetKeydown. Can anyone help me out.

-Thanks, Chris

Input.GetKeyDown() (capital D)