how to bringback an object to its original position after rotation in unity? : i have created a project where a cube is rotated when we touch on it. **i want the cube to return back to its original position** **when the user stopped touching the cube**. here below i have added the source code of rotating a cube. 
please do reply. 
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**SOURCE CODE:-**

using UnityEngine;

using System.Collections;

[RequireComponent(typeof(MeshRenderer))]

public class dr : MonoBehaviour 
{

    #region ROTATE
    private float _sensitivity = 1f;
    private Vector3 _mouseReference;
    private Vector3 _mouseOffset;
    private Vector3 _rotation = Vector3.zero;
    private bool _isRotating;


    #endregion

    void Update()
    {
        if(_isRotating)
        {
            // offset
            _mouseOffset = (Input.mousePosition - _mouseReference); // apply rotation
            _rotation.y = -(_mouseOffset.x + _mouseOffset.y) * _sensitivity; // rotate
            gameObject.transform.Rotate(_rotation); // store new mouse position
            _mouseReference = Input.mousePosition;
        }

    }

    void OnMouseDown()
    {
        // rotating flag
        _isRotating = true;

        // store mouse position
        _mouseReference = Input.mousePosition;
    }

    void OnMouseUp()
    {
        // rotating flag
        _isRotating = false;
    }

}
