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 res = 0;
        long s = (long) k;
        long pos = (s * (s-1))/2L;
        long start = 2L * pos + 1;
        long end = 2L * (pos + s - 1) + 1;
        for(long i = start; i <= end; i += 2)
            res += i;
        return res;
    }

    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();
    }
}