using System;
using System.Collections.Generic;
using System.Text;

public class Program
{
    public void Proc(){
        Reader.IsDebug = false;
        
        long num = long.Parse(Reader.ReadLine());
        
        long masAns = 0;
        for(long i=1; i<num; i++) {
            long baseNum = num - i; // 下の玉の数
            long ans = i * (baseNum + 1);
            ans += baseNum;
            masAns = Math.Max(masAns, ans);
        }
        Console.WriteLine(masAns);


    }
    
    public static void Main(string[] args)
    {
        Program prg = new Program();
        prg.Proc();
    }
}

class Reader
{
    public static bool IsDebug = true;
    
    private static System.IO.StringReader sr;
    
    public static string ReadLine() {
        if(IsDebug) {
            if(sr == null) {
                sr = new System.IO.StringReader(initStr.Trim());
            }
            return sr.ReadLine();
        } else {
            return Console.ReadLine();
        }
    }
    
    public static int[] GetInt(char delimiter = ' ', bool mustTrim = false) {
        string src = ReadLine();
        if(mustTrim) {
            src = src.Trim();
        }
        string[] inpt = src.Split(delimiter);
        int[] ret = new int[inpt.Length];
        for(int i=0; i<inpt.Length; i++) {
            string item = inpt[i];
            if(mustTrim) {
                item = item.Trim();
            }
            ret[i] = int.Parse(item);
        }
        return ret;
    }
    
    private static string initStr = @"

1000000



";
}