How to empty navigation stack for signout

[lifesuxtr]

I am writing signout method for my app.The thing is i want to empty nav stack before signing out but i dont know how ??

signout(){
    //unsubscribtionshere
    this.app.auth().signOut().then(a =>{
        //clear navigation stack
        alert("you successfully signed out");
        this.navCtrl.setRoot(LoginPage); //push user to loginpage
      });
}