1 import java.util.*;
 2 
 3 public class HDOJ_1001 {
 4 
 5     public static void main(String[] args) {
 6         Scanner reader=new Scanner(System.in);
 7         while(reader.hasNext()) {
 8             long n=reader.nextInt();
 9             long sum=((1+n)*n)/2;
10             System.out.println(sum);
11             System.out.println();;
12         }
13     }
14 
15 }