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

public class Solution {

    static long sumOfGroup(int k) {
        // Find odds
		long numbers=0;
		int counter=1;
		int contador=0;
		ArrayList<Long> odds = new ArrayList<Long>();
		for(int i = 0; i < 100000; i++){
			if(!(numbers%2==0)){
				odds.add(numbers);
			}
			numbers++;
		}
		// Determine groups
		for(int i = 0; i < k; i++){
			counter+=contador;
			contador++;
		}
		int index=counter-1;
		long sum=0;
		for(int i = 0; i < k; i++){
			sum+=odds.get(index);
			index++;
		}
		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();
    }
}