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

public class Solution {

    static long sumOfGroup(long k) {
        // Return the sum of the elements of the k'th group.
        long sum = (k * (k-1)) + 1;
        long finalSum = sum;
        long i = k-1;
        while(i > 0){
            sum = (sum + 2);
            finalSum += sum;
            i--;
        }
        return finalSum;
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        long k = in.nextLong();
        long answer = sumOfGroup(k);
        System.out.println(answer);
        in.close();
    }
}