RectangleCalc

 class Rectangle_Calc
    {
        public double width { get; set; }

        public double heigth { get; set; }

        public double AreaCalc
        {
            get
            {
                return width * heigth;
            }
        }
        public double PerimeterCalc
        {
            get
            {
                return 2 * width + 2 * heigth;
            }
        }
        public double DiagonalCalc
        {
            get
            {
                return Math.Sqrt(width * width + heigth * heigth);
            }
        }

        public override string ToString()
        {
            return string.Format("{0}", AreaCalc);
        }

    }




 static void Main(string[] args)
        {
            double widthRec = double.Parse(Console.ReadLine());
            double heightRec = double.Parse(Console.ReadLine());

            Rectangle_Calc rec = new Rectangle_Calc { width = widthRec, heigth = heightRec };

            Console.WriteLine($"Perimater: {rec.PerimeterCalc}");
            Console.WriteLine($"Area: {rec.AreaCalc}");
            Console.WriteLine($"Diagonals: {rec.DiagonalCalc}");
        }