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

public class Solution {

    static long sumOfGroup(int x) {
        // Return the sum of the elements of the k'th group.
        Integer y = x;
        Long k = new Long(y);
        long s;
        if (k % 2 == 0) {
            s = (k/2) * (k-1);
        } else {
            s = k * ((k-1)/2);
        }
        long a = 2*(s+1) - 1;
        long ans = (k*(2*a + (k-1)*2))/2;
        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();
    }
}