help me to save high score??

how should I save highest no of coins which loads when game starts again my code is using UnityEngine; using System.Collections;

public class MouseController : MonoBehaviour {

 public float jetpackForce = 75.0f;

 public float forwardMovementSpeed = 3.0f;

 public Transform groundCheckTransform;
 
 private bool grounded;
 
 public LayerMask groundCheckLayerMask;
 
 Animator animator;

 public ParticleSystem jetpack;

 private bool dead = false;

 private uint coins = 0;

 public Texture2D coinIconTexture;

 public AudioClip coinCollectSound;

 public AudioSource jetpackAudio;
 
 public AudioSource footstepsAudio;

 public ParallaxScroll parallax;

 // Use this for initialization
 void Start () {
     animator = GetComponent<Animator>();    
 }
 
 // Update is called once per frame
 void Update () {
 
 }

 void FixedUpdate () 
 {
     bool jetpackActive = Input.GetButton("Fire1");
     
     jetpackActive = jetpackActive && !dead;
     
     if (jetpackActive)
     {
         GetComponent<Rigidbody2D>().AddForce(new Vector2(0, jetpackForce));
     }
     
     if (!dead)
     {
         Vector2 newVelocity = GetComponent<Rigidbody2D>().velocity;
         newVelocity.x = forwardMovementSpeed;
         GetComponent<Rigidbody2D>().velocity = newVelocity;
     }
     
     UpdateGroundedStatus();
     
     AdjustJetpack(jetpackActive);

     AdjustFootstepsAndJetpackSound(jetpackActive);

     parallax.offset = transform.position.x;
 } 

 void UpdateGroundedStatus()
 {
     //1
     grounded = Physics2D.OverlapCircle(groundCheckTransform.position, 0.1f, groundCheckLayerMask);
     
     //2
     animator.SetBool("grounded", grounded);
 }

 void AdjustJetpack (bool jetpackActive)
 {
     jetpack.enableEmission = !grounded;
     jetpack.emissionRate = jetpackActive ? 300.0f : 75.0f; 
 }

 void OnTriggerEnter2D(Collider2D collider)
 {
     if (collider.gameObject.CompareTag("Coins"))
         CollectCoin(collider);
     else
         HitByLaser(collider);
 }
     
 void HitByLaser(Collider2D laserCollider)
 {
     if (!dead)
         laserCollider.gameObject.GetComponent<AudioSource>().Play();

     dead = true;

     animator.SetBool("dead", true);
 }

 void CollectCoin(Collider2D coinCollider)
 {
     coins++;
     
     Destroy(coinCollider.gameObject);

     AudioSource.PlayClipAtPoint(coinCollectSound, transform.position);
 }

 void OnGUI()
 {
     DisplayCoinsCount();

     DisplayRestartButton();
 }

 void DisplayCoinsCount()
 {
     Rect coinIconRect = new Rect(10, 10, 32, 32);
     GUI.DrawTexture(coinIconRect, coinIconTexture);                         
     
     GUIStyle style = new GUIStyle();
     style.fontSize = 30;
     style.fontStyle = FontStyle.Bold;
     style.normal.textColor = Color.yellow;
     
     Rect labelRect = new Rect(coinIconRect.xMax, coinIconRect.y, 60, 32);
     GUI.Label(labelRect, coins.ToString(), style);
 }

 void DisplayRestartButton()
 {
     if (dead && grounded)
     {
         Rect buttonRect = new Rect(Screen.width * 0.35f, Screen.height * 0.45f, Screen.width * 0.30f, Screen.height * 0.1f);
         if (GUI.Button(buttonRect, "Tap to restart!"))
         {
             Application.LoadLevel (Application.loadedLevelName);
         };
     }
 }

 void AdjustFootstepsAndJetpackSound(bool jetpackActive)    
 {
     footstepsAudio.enabled = !dead && grounded;
     
     jetpackAudio.enabled =  !dead && !grounded;
     jetpackAudio.volume = jetpackActive ? 1.0f : 0.5f;        
 }

}

help me to add the statements to save no. of coins which loads at startup I am new to scripts