using System;
using System.Linq;

class No111
{
    static void Main()
    {
        var length = Int32.Parse(Console.ReadLine());
        var b = length/2;
        long ans = 0;
        if (length % 2 == 1) ans = b;
        for (int i = b - 1; i > 0; --i) ans += (i * 2);
        Console.WriteLine(ans);
    }
}