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

public class Solution {
    
    public static int fact(int k) {
        if(k==1||k==0)
            return 1;
        return k+fact(k-1);
    }
    
    static void sumOfGroup(int k) {
        int n = fact(k-1);
        long ans = 0L;
        int temp = (2*(n+1))-1;
        for(int i = 0; i<k; i++) {
            ans += temp;
            
            temp+=2;
        }
        System.out.println(ans);
    }

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