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

    static long sumOfGroup(int k) {
        var firstIndex = (1.0 + (k-1)) / 2 * (k-1) + 1;
        var lastIndex = firstIndex + k - 1;
        
        return partialSum((long)lastIndex) - partialSum((long)firstIndex - 1);
    }
    
    private static long partialSum(long k) {
        if (k == 0) return 0;
        
        return (1 + 2*k) / 2 * k;
    }

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