using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.Text;
using System.Text.RegularExpressions;
using System.Linq;


class Magatro
{
    static long N = long.Parse(Console.ReadLine());
    static void Main()
    {
        long Ue, Sita;
       Ue = N / 2;
        Sita = N - Ue;
        long ans = Ue * (Sita + 1) + Sita;
        Console.WriteLine(ans);
    }
}