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 kk = Long.valueOf(k);
    		Long first = kk*(kk-1) + 1;
		//System.out.println(first);
		Long dbl = 0L;
		for (Long j=1L; j<kk; j++) {
			dbl = dbl+j;
		}
		//System.out.println(dbl);
		Long result = first * Long.valueOf(k);
		//System.out.println(result);
		Long result2 = Long.valueOf(2 * dbl);
		//System.out.println(result2);
		return result+result2;
    }

    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();
    }
}