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

public class Solution {

    static long sumOfGroup(long k) {
        // Return the sum of the elements of the k'th group.
        long firstElementOfkthGrp = k*k - k + 1;
        long lastElementOfkthGrp = firstElementOfkthGrp + ((k-1)*2);

        long sumOfElementsBeforeThisGrp = (firstElementOfkthGrp-1)/2 * (firstElementOfkthGrp-1)/2;
        long sumOfGroup = ((lastElementOfkthGrp+1)/2 * (lastElementOfkthGrp+1)/2) - sumOfElementsBeforeThisGrp;
        return sumOfGroup;
    }

    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();
    }
}