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

public class Solution {

    static long sumOfGroup(int k) {
       
        long x=0;
        
        for(int i=1;i<=k-1;i++){
            x+=i;
        }
        long value=2*x+1;
        
        long ans=0;
        for(int i=0;i<k;i++){
            ans+=(value);
            value+=2;
        }
        return ans;
    }

    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();
    }
}