Error with script.

I don't know what the error mean. It says Camera does not contain a definition for 'main'. Can someone help me figure this out?

 using UnityEngine;
 using System.Collections;
 
 public class ReticleMovement : MonoBehaviour
 {
     void Update ()
     {
         Ray ray = Camera.Cam.ScreenPointToRay(Input.mousePosition);
         RaycastHit[] hits;
         
         hits = Physics.RaycastAll(ray);
         
         foreach(RaycastHit h in hits)
         {
             if(h.collider.name == "ground")
                 transform.position = new Vector3(h.point.x, 5f, h.point.z);
         }
     }
 }