using System; public class HelloWorld { public static void Main(string[] args) { int score = int.Parse(Console.ReadLine()); if(score >=0 && score = 90) { Console.WriteLine("A"); } else if (score >= 80) { Console.WriteLine("B"); } else if (score >= 70) { Console.WriteLine("C"); } else if (score >= 60) { Console.WriteLine("D"); } else { Console.WriteLine("F"); } } } }