public class Sum
{
  public static void main(String args[])
  {
    int n = Integer.parseInt(args[0]);
   
    int sum = getSum2(n);
    System.out.println(sum);
  }
/*
  public static int getSum(int n)
  {
    int retval = 0;
    for(int i = 1; i <= n; i++)
    {
      retval += i;
    }
    return retval;
  }
*/

  public static int getSum2(int n)
  {
    int retval;
    if(n < 1)
    {
      retval = 0;
    }
    else
    {
      retval = n + getSum2(n-1);
    }
    return retval;
  }
  
}