백준 C# 9498

using System;

namespace baek2
{
    class Program
    {
        static void Main(string[] args)
        {
            string score_input = Console.ReadLine();
            int score = int.Parse(score_input);

            if (score >= 90 && score <= 100) Console.WriteLine("A");
            else if (score >= 80 && score <= 89) Console.WriteLine("B");
            else if (score >= 70 && score <= 79) Console.WriteLine("C");
            else if (score >= 60 && score <= 69) Console.WriteLine("D");
            else Console.WriteLine("F");

        }
    }
}