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

public class Solution {

    static long sumOfGroup(int k) {
        long k1 = k;
        long start = (k1 - 1) * k1 + 1;
        long end = k1 * (k1 + 1) - 1;
        long result = 0;
        while (start <= end) {
            result += start;
            start += 2;
        }
        return result;
    }

    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();
    }
}