Function คำนวณคะแนนนักศึกษา || ลองทำดูแล้วผิดตรงไหนไม่รู้อะครับ ช่วยผมที

static void Main(string[] args)
        {
         Console.Write("Grade = ");
         int Scrore = int.Parse(Console.ReadLine());

         CalculateGrade(Scrore);

         Console.ReadKey();
        }
        static string CalculateGrade(int Scrore)
        {
         if (Scrore < 50)
         {
                Console.Write("Grade F");
         }
         if (Scrore <= 60)
         {
                Console.Write("Grade D");
         }
         if (Scrore <= 70)
         {
                Console.Write("Grade C");
         }
         if (Scrore < 80)
         {
                Console.Write("Grade B");
         }
         if (Scrore >= 80)
         {
                Console.Write("Grade a");
         }
         return array;
        }