Double jumping

Hey, I'm trying to make my player able to double jump, but i haven't had success. Can someone help me out? Here's my script:

using System.Collections; using System.Collections.Generic; using UnityEngine;

[RequireComponent(typeof(CharacterController))] public class Player : MonoBehaviour { public Camera cam; public Animator anim; public CharacterController controller;

 public float movement;
 private float movementspeed;
 public float InputX;
 public float InputZ;
 public float Speed;

 public Vector3 desiredMoveDirection;
 public bool blockRotationPlayer;
 public float allowPlayerRotation;

 private float verticalVel;
 public bool isGrounded;
 public float jumpSpeed;
 public float gravity;
 private Vector3 moveVector;


 void Start()
 {
     anim = this.GetComponent<Animator>();
     controller = this.GetComponent<CharacterController>();
     
 }

 void Update()
 {

     if (controller.isGrounded)
     {
         if (Input.GetButton("Jump"))
         {
             verticalVel = jumpSpeed;
         }
         anim.SetBool("Jump", false);
     }

     else
     {
         anim.SetBool("Jump", true); 
         verticalVel -= gravity * Time.deltaTime;
     }

     InputMovement();

     moveVector = new Vector3(0, verticalVel, 0); 
     controller.Move(moveVector);
 }

 void PlayerMoveAndRotation()
 {
     var forward = cam.transform.forward; 
     var right = cam.transform.right; 

     forward.y = 0f; 
     right.y = 0f; 

     forward.Normalize(); 
     right.Normalize();

     desiredMoveDirection = forward * InputZ + right * InputX; 

     if (blockRotationPlayer == false) 
     {
         transform.rotation = Quaternion.Slerp(transform.rotation, Quaternion.LookRotation(desiredMoveDirection), 0.1f); 
     }
 }

 void InputMovement()
 {
     InputX = Input.GetAxisRaw("Horizontal"); 
     InputZ = Input.GetAxisRaw("Vertical"); 

     movementspeed = movement; 
     controller.Move(desiredMoveDirection * Time.deltaTime * movementspeed); 

     anim.SetFloat("InputZ", InputZ, 0.0f, Time.deltaTime); 
     anim.SetFloat("InputX", InputX, 0.0f, Time.deltaTime); 

     
     Speed = new Vector2(InputX, InputZ).sqrMagnitude; 

     if (Speed == 2)
         Speed = 1;

    
     if (Speed > allowPlayerRotation)
     {
         anim.SetFloat("InputMovement", Speed, .1f, Time.deltaTime); 
         PlayerMoveAndRotation(); 
     }

     else
     {
         anim.SetFloat("InputMovement", Speed, 0.1f, Time.deltaTime); 
         desiredMoveDirection.x = 0;
         desiredMoveDirection.y = 0;
         desiredMoveDirection.z = 0;
     }
 }

}