using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace MarkRank
{
    class Program
    {
        static void Main(string[] args)
        {
            SoluteRank mk = new SoluteRank();
            mk.GetMark(0);
            mk.Rank();
            Console.ReadKey();

        }
    }

    class SoluteRank
    {
        private double mark;
        public void GetMark(double m)
        {
            Console.WriteLine("请输入成绩");
            m = Convert.ToDouble(Console.ReadLine());
            mark = m;
        }
        public void Rank()
        {
            if (mark < 0 || mark > 100)
            {
                Console.WriteLine("输入错误");
                return;
            }
            if (mark >= 90) Console.WriteLine("优");
            else if (mark >= 80) Console.WriteLine("良");
            else if (mark >= 60) Console.WriteLine("中");
            else Console.WriteLine("差");

        }
    }

}