Google login button whit firebase in android studio, error: cannot find symbol variable default_web_client_id

I try to use google sign in button(suggested with firebase) in my android app like this:

        GoogleSignInOptions gso = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
            .requestIdToken(getString(R.string.default_web_client_id))
            .requestEmail()
            .build();
    // [END config_signin]

    mGoogleApiClient = new GoogleApiClient.Builder(this)
            .enableAutoManage(this /* FragmentActivity */, this /* OnConnectionFailedListener */)
            .addApi(Auth.GOOGLE_SIGN_IN_API, gso)
            .build();

But return this error : Error:(112, 51) error: cannot find symbol variable default_web_client_id

If I try to modify my R directory, I can't, so I'm stuck. In the earlier version of my app in the R file, I've public static final int default_web_client_id=0x7f060079;