import java.util.*;
public class Main {
    public static void main (String[] arg) {
        
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        
        int r = 0;
        
        for(int i=0; i<a; i++) {
            r += i+1;
        }
        
        System.out.println(r);
    }
}