value.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
    long v= (long) dataSnapshot.getValue();
    CountDownTimer countDownTimer=new CountDownTimer(v,1000) {
        @Override
        public void onTick(long millisUntilFinished) {
            show.setText("time : "+millisUntilFinished/1000);
        }
        @Override
        public void onFinish() {
            Intent i=new Intent(Main4Activity.this,OneActivity.class);
            startActivity(i);
        }
    }.start();
}
@Override
public void onCancelled(DatabaseError databaseError) {

}