I am trying to add sprinting ability to my attempt of a game I got movement done but cant get sprint

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

public class PlayerMovement : MonoBehaviour
{
    public CharacterController controller;

    public float speed = 6f;
    public float gravity = -20;
    public float jumpHeight = 3f;

    public Transform groundCheck;
    public float groundDistance = 0.4f;
    public LayerMask groundMask;

    public bool isMoving = false;
    public float movementSpeed = 200;

    Vector3 velocity;
    bool isGrounded;

    void Update()
    {
        isGrounded = Physics.CheckSphere(groundCheck.position, groundDistance, groundMask);

        if (isGrounded && velocity.y < 0)
        {
            velocity.y = -2f;
        }

        float x = Input.GetAxis("Horizontal");
        float z = Input.GetAxis("Vertical");

        if (Input.GetKeyDown("w"))
        {
            isMoving = true;
        }

        if (Input.GetKeyUp("w"))
        {
            isMoving = false;
        }

        

            Vector3 move = transform.right * x + transform.forward * z;

        controller.Move(move * speed * Time.deltaTime);

        if (Input.GetButtonDown("Jump") && isGrounded)
        {
            velocity.y = Mathf.Sqrt(jumpHeight * -2f * gravity);
        }

        if (Input.GetKey(KeyCode.LeftShift) & isMoving == true)

        {
            transform.position += transform.forward * Time.deltaTime * movementSpeed;
        }

        velocity.y += gravity * Time.deltaTime;

        controller.Move(velocity * Time.deltaTime);
    }
}

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

public class PlayerMovement : MonoBehaviour
{
    public CharacterController controller;

    public float speed = 6f;
    public float gravity = -20;
    public float jumpHeight = 3f;

    public Transform groundCheck;
    public float groundDistance = 0.4f;
    public LayerMask groundMask;

    public bool isMoving = false;
    public float movementSpeed = 200;

    Vector3 velocity;
    bool isGrounded;

    void Update()
    {
        isGrounded = Physics.CheckSphere(groundCheck.position, groundDistance, groundMask);

        if (isGrounded && velocity.y < 0)
        {
            velocity.y = -2f;
        }

        float x = Input.GetAxis("Horizontal");
        float z = Input.GetAxis("Vertical");

        if (Input.GetKeyDown("w"))
        {
            isMoving = true;
        }

        if (Input.GetKeyUp("w"))
        {
            isMoving = false;
        }

        

            Vector3 move = transform.right * x + transform.forward * z;

        controller.Move(move * speed * Time.deltaTime);

        if (Input.GetButtonDown("Jump") && isGrounded)
        {
            velocity.y = Mathf.Sqrt(jumpHeight * -2f * gravity);
        }

        if (Input.GetKey(KeyCode.LeftShift) & isMoving == true)

        {
            transform.position += transform.forward * Time.deltaTime * movementSpeed;
        }

        velocity.y += gravity * Time.deltaTime;

        controller.Move(velocity * Time.deltaTime);
    }
}