The namespace `global::' already contains a definition for `ShooterGameCamera'

error at line "public class ShooterGameCamera : MonoBehaviour {" this is upper part of script ShooterGameCamera.cs taken from 3rdpersonshooter unity demo game

using UnityEngine; using System.Collections;

 // 3rd person game-like camera controller
 // keeps camera behind the player and aimed at aiming point
 public class ShooterGameCamera : MonoBehaviour {
     
     public Transform player;
     public Transform aimTarget;
     
     public float smoothingTime = 0.5f;
     public Vector3 pivotOffset = new Vector3(1.3f, 0.4f,  0.0f);
     public Vector3 camOffset   = new Vector3(0.0f, 0.7f, -2.4f);
     public Vector3 closeOffset = new Vector3(0.35f, 1.7f, 0.0f);
     
     public float horizontalAimingSpeed = 270f;
     public float verticalAimingSpeed = 270f;
     public float maxVerticalAngle = 80f;
     public float minVerticalAngle = -80f;
     
     public float mouseSensitivity = 0.1f;
     
     public Texture reticle;
     
     private float angleH = 0;
     private float angleV = 0;
     private Transform cam;
     private float maxCamDist = 1;
     private LayerMask mask;
     private Vector3 smoothPlayerPos;