How can i put a camera border in this script?

using System;
using UnityEngine;

namespace UnityStandardAssets._2D
{
public class Camera2DFollow : MonoBehaviour
{
public Transform target;
public float damping = 1;
public float lookAheadFactor = 3;
public float lookAheadReturnSpeed = 0.5f;
public float lookAheadMoveThreshold = 0.1f;

    private float m_OffsetZ;
    private Vector3 m_LastTargetPosition;
    private Vector3 m_CurrentVelocity;
    private Vector3 m_LookAheadPos;

    // Use this for initialization
    private void Start()
    {
        m_LastTargetPosition = target.position;
        m_OffsetZ = (transform.position - target.position).z;
        transform.parent = null;
    }

    // Update is called once per frame
    private void Update()
    {
        // only update lookahead pos if accelerating or changed direction
        float xMoveDelta = (target.position - m_LastTargetPosition).x;

        bool updateLookAheadTarget = Mathf.Abs(xMoveDelta) > lookAheadMoveThreshold;

        if (updateLookAheadTarget)
        {
            m_LookAheadPos = lookAheadFactor*Vector3.right*Mathf.Sign(xMoveDelta);
        }
        else
        {
            m_LookAheadPos = Vector3.MoveTowards(m_LookAheadPos, Vector3.zero, Time.deltaTime*lookAheadReturnSpeed);
        }

        Vector3 aheadTargetPos = target.position + m_LookAheadPos + Vector3.forward*m_OffsetZ;
        Vector3 newPos = Vector3.SmoothDamp(transform.position, aheadTargetPos, ref m_CurrentVelocity, damping);

        transform.position = newPos;

        m_LastTargetPosition = target.position;
    }

}

}

Take a look here: Creating 2D Games in Unity 4.5 #15 - Camera Controller - YouTube