how to run Storyboard synchronously

how can i make this code run synchronously?

        private void slide_anim1(int from, int to, string direction)
        {
            Duration d = new Duration(new TimeSpan(0, 0, 0, 0, 300));
            Storyboard sb = new Storyboard();
            DoubleAnimation da1, da2;
            if (direction == "in")
            {
                da1 = new DoubleAnimation(from, to, d);
                da2 = new DoubleAnimation(1, 0, d);
                da1.EasingFunction = da2.EasingFunction = new SineEase();
                Storyboard.SetTargetProperty(da1, new PropertyPath("(Canvas.Top)"));
                Storyboard.SetTargetProperty(da2, new PropertyPath("(Opacity)"));
            }
            else {
                da1 = new DoubleAnimation(from, to, d);
                da2 = new DoubleAnimation(0, 1, d);
                da1.EasingFunction = da2.EasingFunction = new BackEase();
                Storyboard.SetTargetProperty(da1, new PropertyPath("(Canvas.Top)"));
                Storyboard.SetTargetProperty(da2, new PropertyPath("(Opacity)"));
            }
            sb.Children.Add(da1);
            sb.Children.Add(da2);
            Storyboard.SetTarget(sb, main_grid);
            sb.Begin();
        }

I can't use the .Completed event in my context, because the function that usesslide_anim1 has to return something only, but ONLY, when the animation finishes.