import  java.io.*;
public  class  Sum
{
	public static void main (String[] args)
	{
       int   i , n=-1 , sum=0 ;
       while ( n<1)
       try {
          BufferedReader  br =
new BufferedReader( new  InputStreamReader(System.in));
          n = Integer.parseInt(br.readLine( ));
       } catch ( IOException  e ) { } ;
       for  ( i =1 ; i<=n; i++ )      sum += i;
       System.out.println(sum);
	}
 }