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

public class Solution {

    static long sumOfGroup(int k) {
        int init = (k*(k-1))+1;
    	int arr[] = new int[k];
    	arr[0]=init;
    	for(int i=1;i<k;i++){
    		arr[i] = arr[i-1]+2;
    		
    	}
    	int sum = 0;
    	for(int val : arr){
    		sum+=val;
    	}
    	
    	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();
    }
}