/*80% or more: A 

70% to less than 80%: B 

60% to less than 70%: C 

50% to less than 60%: D 

45% to less than 50%: E 

0% to less than 45%: F */

​

using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Enter Mark1:");

        int Mark1 = int.Parse(Console.ReadLine());

        Console.WriteLine("Enter Mark2:");

        int Mark2 = int.Parse(Console.ReadLine());

        double Avg = 0;

        char S = ' ';

        if((Mark1 < 0)||(Mark1 > 100) || (Mark2 < 0)||(Mark2 > 100))

        {

            Console.WriteLine("Invalid imput");

        }

        else

        {

            Avg = (Mark1 + Mark2)/2.0;

            if(Avg >= 80)

            {

                S = 'A';

                Console.WriteLine("You achieved " + S);

            }

            else if(Avg >= 70 && Avg < 80)

            {

                S = 'B';

                Console.WriteLine("You achieved " + S);

            }

            else if(Avg >= 60 && Avg < 70)

            {

                S = 'C';

                Console.WriteLine("You achieved " + S);

            }

            else if(Avg >= 50 && Avg < 60)

            {   

                S = 'D';

                Console.WriteLine("You achieved " + S);

            }

            else if(Avg >= 40 && Avg < 50)

            {

                S = 'E';

                Console.WriteLine("You achived " + S);

            }

            else

            {

                S = 'F';

                Console.WriteLine("You failed");

            }

        }

    }

}