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.
        int elem = 1;
        for(int i = 1; i < k; i++)
            elem += i;
        elem = elem * 2 - 1;
        int sum = elem;
        while(k > 1){
            elem += 2;
            sum += elem;
            k--;
        }
        return sum;
    }

    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();
    }
}