using System;

class Program
{
    static void Main()
    {
        var n = long.Parse(Console.ReadLine());
        if (n % 2 == 0) Console.WriteLine(calc(n / 2, n / 2));
        else Console.WriteLine(calc(n / 2, n / 2 + 1));
    }

    static long calc(long a,long b)
    {
        return (a + 1) * b + a;
    }
}