import java.math.BigInteger;
import java.util.Scanner;

class Main {
	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();
	}

	static long sumOfGroup(long k) {
		long high = k*(k+1)/2;
		long low = k*(k-1)/2;
		
		if(k <= 1000) {
			return high*high - low*low;
		} else {
			BigInteger bigHigh = BigInteger.valueOf(high);
			BigInteger bigLow = BigInteger.valueOf(low);
			
			return bigHigh.multiply(bigHigh).subtract(bigLow.multiply(bigLow)).longValue();
		}
	}
}