import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int sum = 0;
		for(int i=n;i>0;i--) {
			sum = sum+i;
		}
		System.out.println(sum);
	}

}

/**************************************************************
	Problem: 2100
	User: admin
	Language: Java
	Result: Accepted
	Time:4169 ms
	Memory:40288 kb
****************************************************************/