<image>

Input

The input contains a single integer a (1 ≤ a ≤ 18257).

Output

Print a single integer output (1 ≤ output ≤ 2·109).

Examples

Input

2


Output

13
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

public class Solution {
    //<editor-fold desc="input parse" defaultstate="collapsed">

    private static StringTokenizer st;
    private static BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

    private static long nextLong() {
        return Long.parseLong(st.nextToken());
    }

    private static int nextInt() {
        return Integer.parseInt(st.nextToken());
    }

    private static double nextDouble() {
        return Double.parseDouble(st.nextToken());
    }

    private static short nextShort() {
        return Short.parseShort(st.nextToken());
    }

    private static byte nextByte() {
        return Byte.parseByte(st.nextToken());
    }

    private static void initTokenizer() throws Exception {
        st = new StringTokenizer(reader.readLine());
    }

    //</editor-fold>

    public static void main(String[] args) throws Exception {
        initTokenizer();

        int a = nextInt();

        if (a == 1) {
            System.out.print(1);
            return;
        }

        int sum = 1;
        int cur = 12;

        for (int i = 1; i < a; i++) {
            sum += cur;
            cur += 12;
        }

        System.out.println(sum);
    }
}