Move the camera only until a certain position

https://scontent.fmgf1-2.fna.fbcdn.net/v/t34.0-12/15870843_1543174992374352_1359602831_n.gif?oh=dc048c9e04617007c5e82379fd5a9c1a&oe=586CC623

Can you see the blue area in this gif? I want block the camera when the player go more to left, to not see the blue area. This is the code that I'm using to move the camera:

 using UnityEngine;
 using System.Collections;
 
 public class configuracoesDaCamera : MonoBehaviour {
 
     Vector3 hit_position = Vector3.zero;
     Vector3 current_position = Vector3.zero;
     Vector3 camera_position = Vector3.zero;
     float z = 0.0f;
     public static bool bDedoNoHud;
 
     void Update()
     {
         if (Input.GetMouseButtonDown(0))
         {
             hit_position = Input.mousePosition;
             camera_position = transform.position;
 
         }
         if (Input.GetMouseButton(0))
         {
             current_position = Input.mousePosition;
             LeftMouseDrag();
         }
         Debug.Log("bDedoNoHud" + bDedoNoHud);
     }
 
     void LeftMouseDrag()
     {
         if (!bDedoNoHud)
         {
             // From the Unity3D docs: "The z position is in world units from the camera."  In my case I'm using the y-axis as height
             // with my camera facing back down the y-axis.  You can ignore this when the camera is orthograhic.
             current_position.z = hit_position.z = camera_position.y;
 
             // Get direction of movement.  (Note: Don't normalize, the magnitude of change is going to be Vector3.Distance(current_position-hit_position)
             // anyways.  
             Vector3 direction = Camera.main.ScreenToWorldPoint(current_position) - Camera.main.ScreenToWorldPoint(hit_position);
 
             // Invert direction to that terrain appears to move with the mouse.
             direction = direction * -1;
 
             Vector3 position = camera_position + direction;
 
             transform.position = position;
         }           
     }
 }