Character rotation (click-to-move)

Hello! I'm new in Unity3D and I have this code:

 private NavMeshAgent agent;
 private Animator anim;

 void Start() {
     agent = GetComponent<NavMeshAgent>();
     anim = GetComponent<Animator> ();
 }

 void Update() {
     RaycastHit hit;
     if (Input.GetMouseButtonDown(0)) {
         Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
         if (Physics.Raycast(ray, out hit))
             agent.SetDestination(hit.point);
             anim.Play ("walk");
     }

     if (!agent.pathPending)
     {
         if (agent.remainingDistance <= agent.stoppingDistance)
         {
             if (!agent.hasPath || agent.velocity.sqrMagnitude == 0f)
             {
                 anim.Play ("idle");
             }
         }
     }
 }

When I click behind of my character my character is rotating slow. I want to character change rotation to go instantly only in front. If I click behind, character to have already roation and only go, without any rotation. Anyone can help me? Thank you!