My Else if statement is not working properly what is the issue?

i am new in C# and understanding how the if statement works i wrote these code but there seems to be a problem with it.When i write something that is 50 or greater and less then 60 it says Passed but the else if statement is not working.Whenever i write something greater then 60 nothing happens my program closes.

        Console.WriteLine("Please state your marks........");
        string uservalue = Console.ReadLine();
        int x = Convert.ToInt32(uservalue);

        if (x >=50)
        {
            if ( x <= 59)
            {
            Console.WriteLine("You Passed");
            }
        }
        else if (x >=60)
        {
            Console.WriteLine("Passed Grade B");
        }
        Console.ReadLine();