import java.util.Scanner;

public class Main {

    public static void main(String[] args) {

    	Scanner sc = new Scanner(System.in);
    	int num = sc.nextInt();
    	int ans = 0;
    	for(int i=1;i<=num;i++){
    		ans += i;
    	}
    	System.out.println(ans);
    }

}