Câu 1
        static void Main(string[] args)
        {
            Console.WriteLine("Hay nhap chieu cao (m)");
            double chieuCao = double.Parse(Console.ReadLine());
            Console.WriteLine("Hay nhap can nang (kg)");
            double canNang = double.Parse(Console.ReadLine());
            double BMI = canNang / Math.Pow(chieuCao,2);
            Console.WriteLine("BMI = {0:0.00}", BMI);
            if(BMI < 18.5)
            {
                Console.WriteLine("Thieu Can");
            }
            else if(BMI <23)
            {
                Console.WriteLine("Binh Thuong");
            }
            else
            {
                Console.WriteLine("Thua Can");
            }
        }