using System;
 
public class Test
{
	public static void Main()
	{
		// your code goes here
	}
}

dXNpbmcgU3lzdGVtOwoKcHVibGljIGNsYXNzIFRlc3QKewoJcHVibGljIHN0YXRpYyB2b2lkIE1haW4oKQoJewoJCS8vIHlvdXIgY29kZSBnb2VzIGhlcmUKCX0KfQ==

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

int mark ;
            Console.Write(" Enter your mark : ");
            while(!int.TryParse(Console.ReadLine() , out mark))
            {
                Console.WriteLine("Please! Enter Number :");
            }
            if( mark >= 90 && mark <= 100 )
            {
                Console.WriteLine(" Grade is A ");
                
            }
            else if ( mark < 90 && mark >= 70 ) 
            {
                Console.WriteLine(" Grade is B ");
            }
            else if ( mark < 70 && mark >= 60 ) 
            {
                Console.WriteLine(" Grade is C ");
            }
            else if ( mark < 60 && mark >= 50 ) 
            {
                Console.WriteLine(" Grade is D ");
            }
            else
            {
            Console.WriteLine(" Grade is F ");
            }