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 s = k*(k+1)/2;
        long val=0;
        for(long i=1;i<=s;i+=2) {
            val = i;
        }
        val+=2;
        //System.out.println("Value : "+val);
        long sum = 0;
        for(long i=1;i<=k;i++) {
            sum+=val;
            val+=2;
        }
        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();
    }
}