1.1

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

namespace _1._1
{
    class Program
    {
        static void Main(string[] args)
        {
            int n, i, result = 0;                       //定义变量
            Console.WriteLine("请输入一个正整数");     
            n = int.Parse(Console.ReadLine());          //输入整数n
            if (n % 2 == 0)                             //判断n奇偶性
                i = 2;
            else
                i = 1;
            for (; i <= n; i += 2)                     //计算i+（i+2）+（i+2+2）+....+n
                result += i;
            Console.WriteLine(result);
            Console.WriteLine("按回车键结束");
            Console.ReadLine();
        }
    }
}