calculate convex hull in csharp

main.cs
using System;
using System.Collections.Generic;
using System.Linq;

namespace ConvexHull
{
    public class Point
    {
        public int X { get; set; }
        public int Y { get; set; }
    }

    public static class ConvexHull
    {
        private static int CrossProduct(Point o, Point a, Point b)
        {
            return (a.X - o.X) * (b.Y - o.Y) - (a.Y - o.Y) * (b.X - o.X);
        }

        public static List<Point> GetConvexHull(List<Point> points)
        {
            if (points.Count <= 1)
                return points;

            var sortedPoints = points.OrderBy(p => p.X).ThenBy(p => p.Y).ToList();

            var lower = new List<Point>();
            for (var i = 0; i < sortedPoints.Count; i++)
            {
                while (lower.Count >= 2 && CrossProduct(lower[lower.Count - 2], lower[lower.Count - 1], sortedPoints[i]) <= 0)
                    lower.RemoveAt(lower.Count - 1);

                lower.Add(sortedPoints[i]);
            }

            var upper = new List<Point>();
            for (var i = sortedPoints.Count - 1; i >= 0; i--)
            {
                while (upper.Count >= 2 && CrossProduct(upper[upper.Count - 2], upper[upper.Count - 1], sortedPoints[i]) <= 0)
                    upper.RemoveAt(upper.Count - 1);

                upper.Add(sortedPoints[i]);
            }

            upper.RemoveAt(0);
            lower.RemoveAt(lower.Count - 1);

            return lower.Concat(upper).ToList();
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            /* Example usage: */
            var points = new List<Point>()
            {
                new Point { X = 1, Y = 1 },
                new Point { X = 2, Y = 3 },
                new Point { X = 3, Y = 2 },
                new Point { X = 4, Y = 4 },
                new Point { X = 5, Y = 1 },
                new Point { X = 6, Y = 3 },
                new Point { X = 7, Y = 2 },
                new Point { X = 8, Y = 4 },
                new Point { X = 9, Y = 1 },
            };

            var convexHull = ConvexHull.GetConvexHull(points);
            foreach (var point in convexHull)
            {
                Console.WriteLine($"({point.X}, {point.Y})");
            }
        }
    }
}
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