Cube Movement

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

public class MoveCube : MonoBehaviour
{
    public float speed;

    // Update is called once per frame
    void Update()
    {
        Vector3 offset = Vector3.zero;

        if (Input.GetKey(KeyCode.LeftShift))
        {
            if (Input.GetKey(KeyCode.UpArrow))
            {
                offset += Vector3.forward;
            }
            if (Input.GetKey(KeyCode.DownArrow))
            {
                offset -= Vector3.forward;
            }
        }
        else
        {
            if (Input.GetKey(KeyCode.UpArrow))
            {
                offset += Vector3.up;
            }
            if (Input.GetKey(KeyCode.DownArrow))
            {
                offset -= Vector3.up;
            }
        }

        if (Input.GetKey(KeyCode.LeftArrow))
        {
            offset -= Vector3.right;
        }

        if (Input.GetKey(KeyCode.RightArrow))
        {
            offset += Vector3.right;
        }

        // apply offset
        transform.position += offset * Time.deltaTime * speed;
    }
}