tank reverse control

greetings everyone,
can anyone give a a tip how to invert A and D while pressed S,so it behaves like most of the keyboard controlled car games? here is the code i copied from tutorial. thx

using UnityEngine;
using System.Collections;

publicclassbasicMovement:MonoBehaviour{
publicfloatmoveSpeed=1f;
publicfloatturnSpeed=30f;

//Usethisfor initialization
voidStart(){
}

//Updateiscalledonceper frame
voidUpdate(){

if(Input.GetKey(KeyCode.W))
transform.Translate(Vector3.forward*moveSpeed*Time.deltaTime);
if(Input.GetKey(KeyCode.S))
transform.Translate(-Vector3.forward*moveSpeed*Time.deltaTime);
if(Input.GetKey(KeyCode.A))
transform.Rotate(-Vector3.up*turnSpeed*Time.deltaTime);
if(Input.GetKey(KeyCode.D))
transform.Rotate(Vector3.up*turnSpeed*Time.deltaTime);
}
}