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

public class Solution {

    static long sumOfGroup(int k) {
        // Return the sum of the elements of the k'th group.
        long last = k*(k+1l)-1;
//        System.out.println("Last "+last);
        long index = last/2 + 1l;
//        System.out.println("Index "+index);
        long pre = (k-1l)*k;
        long preIndex = pre/2 ;
//        System.out.println("Index "+preIndex);
        long ans = index*index - preIndex*preIndex;
        return ans;
    }

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