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

public class Solution {

    static long sumOfGroup(int k) {
        // Return the sum of the elements of the k'th group.
        return 0;
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int k = in.nextInt()+1;
        int aux = 0;
        int last = 0;
        int[] ans = new int[50000];
        for(int i = 0; i<50000;i++){
            ans[i] = (2*i)+1;
        }
        long answer = 0;
        for(int i = 0; i<k-1 ;i++){
            aux=aux+i;
        }
        for(int i = 0; i<k ;i++){
            last=last+i;
        }
        for(int i = aux; i<last;i++){
            answer = answer + ans[i];
        }
        System.out.println(answer);
        in.close();
    }
}