using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
class Solution {

    static long sumOfGroup(int k) {
        
        int total = 0;
        
        for(int m=1;m<=k;m++)
        {
            total = total + m;
        }
        
        int[] PrimeArray = new int [total];
        
        int index = 0;
        for (int i = 1;; i=i+2)
        {
            PrimeArray[index] = i;
            index++;

            if(index == total)
            {
                break;
            }
        }
        
        int StartArray = total - k;
        int EndArray = total - 1;
        int SumTotal = 0;
        
        //Console.Write("\t Total " + total);
        //Console.Write("\t StartArray " + StartArray);
        //Console.Write("\t EndArray " + EndArray);
        
        for(int i=StartArray;i<=EndArray;i++)
        {
            //Console.Write("\t tte" + PrimeArray[1]);
            //Console.Write("\t" + PrimeArray[i]);
            SumTotal = SumTotal + PrimeArray[i];    
        }
        
        return SumTotal;
        // Return the sum of the elements of the k'th group.
    }

    static void Main(String[] args) {
        int k = Convert.ToInt32(Console.ReadLine());
        long answer = sumOfGroup(k);
        Console.WriteLine(answer);
    }
}