import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {

    static long sumOfGroup(long k) {
        // Return the sum of the elements of the k'th group.
        long endTerm = k * (k + 1) / 2;
        long startTerm = endTerm - k;
        long endSeq = 1 + (endTerm - 1) * 2;
        long startSeq = 1 + (startTerm - 1) * 2;
        return (endTerm * (1 + endSeq) / 2) - (startTerm * (1 + startSeq) / 2);
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        long k = in.nextInt();
        long answer = sumOfGroup(k);
        System.out.println(answer);
        in.close();
    }
}