using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;

class Program
{
    public static void Main()
    {
        var n = ulong.Parse(ReadLine());
        var n2 = n + 1;
        if (n % 2 == 0) n /= 2;
        else n2 /= 2;
        WriteLine(n * n2);
    }
}