using System;

public class Hello
{
    public static void Main()
    {
        var n = long.Parse(Console.ReadLine().Trim());
        var ans = 0L;
        for (long i = 1; i <= n -1; i++)
        {
            var t = (i + 1) * (n - i) + i;
            ans = Math.Max(ans, t);
        }
        Console.WriteLine(ans);
    }
}