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 start = (k*(k-1))+1;
    	long sum = start;
    	for (long i=1; i <k; i++) {
    		start = start+2;
    		sum = sum + start;
    	}
    	
    	return sum;    	
    	
    }

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